which 2 to 4 openings to focus on as a 500+ rated player

"... For players with very limited experience, I recommend using openings in which the play can be clarified at an early stage, often with a degree of simplification. To accomplish this safely will take a little study, because you will have to get used to playing wiith open lines for both sides' pieces, but you can't eliminate risk entirely in the opening anyway. ... teachers all over the world suggest that inexperienced players begin with 1 e4. ... You will undoubtedly see the reply 1 ... e5 most often when playing at or near a beginner's level, ... After 2 Nf3, 2 ... Nc6 will occur in the bulk of your games. ... I recommend taking up the classical and instructive move 3 Bc4 at an early stage. Then, against 3 ... Bc5, it's thematic to try to establish the ideal centre by 4 c3 and 5 d4; after that, things can get complicated enough that you need to take a look at some theory and learn the basics; ... Of course, you can also play 1 d4 ... A solid and more-or-less universal set-up is 2 Nf3 and 3 Bf4, followed in most cases by 4 e3, 5 Be2 and 6 0-0. I'd rather see my students fight their way through open positions instead; however, if you're not getting out of the opening alive after 1 e4, this method of playing 1 d4 deserves consideration. ... a commonly suggested 'easy' repertoire for White with 1 Nf3 and the King's indian Attack ... doesn't lead to an open game or one with a clear plan for White. Furthermore, it encourages mechanical play. Similarly, teachers sometimes recommend the Colle System ..., which can also be played too automatically, and usually doesn't lead to an open position. For true beginners, the King's Indian Attack and Colle System have the benefit of offering a safe position that nearly guarantees passage to some kind of playable middlegame; they may be a reasonable alternative if other openings are too intimidating. But having gained even a small amount of experience, you really should switch to more open and less automatic play." - IM John Watson in a section of his 2010 book, Mastering the Chess Openings, Volume 4

"As Black, I think that [players with very limited experience] would do well … playing 1...e5 versus 1 e4 and 1...d5 versus 1 d4. … [After 1 d4 d5, if] White plays the most important move, 2 c4, inexperienced players might want to begin classically with 2...e6 followed by ...Nf6 and ...Be7 …" - IM John Watson (2010)

Perhaps it would be a good idea to start with Discovering Chess Openings, a book about opening principles.
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

Here are some books that set out to help the reader to choose specific openings:

Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/

https://www.chess.com/blog/ForwardChess/book-of-the-week-openings-for-amateurs
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf

First Steps: 1 e4 e5
https://www.newinchess.com/media/wysiwyg/product_pdf/7790.pdf

https://chesscafe.com/book-reviews/first-steps-1-e4-e5-by-john-emms/

First Steps: Queen's Gambit

https://www.newinchess.com/media/wysiwyg/product_pdf/7652.pdf

My First Chess Opening Repertoire for White
https://www.newinchess.com/media/wysiwyg/product_pdf/9033.pdf
https://chessbookreviews.wordpress.com/tag/vincent-moret/
Opening Repertoire 1 e4
https://www.newinchess.com/media/wysiwyg/product_pdf/7819.pdf

Yasser Seirawan's Winning Chess Openings
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf

Be sure to try to use the openings in games in between sessions of learning. Most of the time, one faces a position with no knowledge of a specific move indicated in a book. One has to accept that as part of chess, and think of opening knowledge as a sometimes helpful aid. After a game, it makes sense to try to look up the moves in a book and see if it has some indication of how one might have played better in the opening. Many opening books are part explanation and part reference material. The reference material is included in the text with the idea that one mostly skips it on a first reading, and looks at an individual item when it applies to a game that one has just played. Resist the temptation to try to turn a book into a mass memorization project. There are many important subjects that one should not neglect because of too much time on opening study.
https://www.chess.com/article/view/learning-an-opening-to-memorize-or-understand
"... Overall, I would advise most players to stick to a fairly limited range of openings, and not to worry about learning too much by heart. ..." - FM Steve Giddins (2008)
"... I feel that the main reasons to buy an opening book are to give a good overview of the opening, and to explain general plans and ideas. ..." - GM John Nunn (2006)
"... If the book contains illustrative games, it is worth playing these over first ..." - GM John Nunn (2006)
"... the average player only needs to know a limited amount about the openings he plays. Providing he understands the main aims of the opening, a few typical plans and a handful of basic variations, that is enough. ..." - FM Steve Giddins (2008)
"... Everyman Chess has started a new series aimed at those who want to understand the basics of an opening, i.e., the not-yet-so-strong players. ... I imagine [there] will be a long series based on the premise of bringing the basic ideas of an opening to the reader through plenty of introductory text, game annotations, hints, plans and much more. ..." - FM Carsten Hansen (2002)
https://web.archive.org/web/20140627055734/http://www.chesscafe.com/text/hansen38.pdf
"... The way I suggest you study this book is to play through the main games once, relatively quickly, and then start playing the variation in actual games. Playing an opening in real games is of vital importance - without this kind of live practice it is impossible to get a 'feel' for the kind of game it leads to. There is time enough later for involvement with the details, after playing your games it is good to look up the line. ..." - GM Nigel Davies (2005)
"... Review each of your games, identifying opening (and other) mistakes with the goal of not repeatedly making the same mistake. ... It is especially critical not to continually fall into opening traps – or even lines that result in difficult positions ..." - NM Dan Heisman (2007)
https://web.archive.org/web/20140627062646/http://www.chesscafe.com/text/heisman81.pdf

Chess Openings Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond

https://www.chess.com/blog/RussBell

Play the London System (d4 followed by Bf4). It's solid and easy to play!

"... for those that want to be as good as they can be, they'll have to work hard.
Play opponents who are better than you … . Learn basic endgames. Create a simple opening repertoire (understanding the moves are far more important than memorizing them). Study tactics. And pick up tons of patterns. That’s the drumbeat of success. ..." - IM Jeremy Silman (December 27, 2018)
https://www.chess.com/article/view/little-things-that-help-your-game

1. e4

1. f3 should work just as well as the others at your level.

Hey @scouterr

In my opinion there are only a couple things 500 players should focus on:

1. Refuting the Parham attack (2. Bc4... 3. Qh5). It's easily repelled once understood, but a 500 will lose a lot of games not understanding how to counter it. 

2. Opening principles are more important than opening theory... Control of the center, active (but safe) pieces, safe king. That said...

For white, the London is a good start, it's a rock solid setup and operates SOMEWHAT independently of what your opponent does. The flip side is that for beginner players, once your setup is complete, a London can be a little hard to find something to do in (after your setup, what comes next?), but at least you'll get the plane off the ground.

For  beginners playing as black, I found either the Pirc or Caro Kahn to be good starters. The flip side of these is that they cost you a little space, but you don't usually fall victim to low level Patzer tricks. Again, with these systems at least you're not lost before even getting to the middle game. 

You'll see advice that critcizes some of these, but often that advice comes from people who forget what it's like to play in the 500 range... and they also forget that plenty of pro players have used these systems over time. 

3. Spend time with tactics as well as openings. You'll start seeing opportunities in other parts of the game.

4. Play slow. Bullet Chess is no place for the 500 range. 

Hope that helps.

First of all 1.e4 is the only way for you from now on. Why 1.e4? The reason 1.e4 is so widely suggested by players (even though some of them don't really know why) is because 1.e4 offers so many different pawn structures. You will need that kind of experience to improve in the game and appreciate different types of the game (how to play in open or closed positions). 1.e4 will force you to play good moves and it will also introduce you to many tactical motifs in the game. Probably the biggest reason for you to play 1.e4 is to appreciate the TIME. Time is the one of the most important things in chess you have to get familiar with. Once you appreciate the time, you will start to understand openings better and on a whole new level actually. 1.e4 e5 is the way to go with Black and against 1.d4 you play 1...d5. If I were you I would get some books on mates in one, two and three. Basically keep playing and solving puzzles until you reach 1500. Then, I will give you some more suggestions. Well, I hope you'll take my advice and start improving.

There is no point in learning any particular opening at this level. Because your opponent is likely to deviate from the book at move 2!

The most important thing is to learning opening principles as one or two others have mentioned. These are really simple:

1. Move pawns before pieces

2. Move central pawns first

3. Develop knights before bishops

4. Look to castle

A nice list and explanation is given here -https://www.chessstrategyonline.com/content/tutorials/how-to-start-a-game-of-chess-opening-principles

If you follow these principles you will be fine no matter what your opponent plays. 

Note, however, that at the 500 level openings don't decide games. The player who loses is the one who most frequently fails to notice that their opponent can capture their piece or who fails to notice that they can capture an opponent's piece. In other words .... study tactics.