don't learn openings. it's a waste of time. If you really want to have a tool to memorise openings, then you should buy a chessable opening repertoire
What's a good way to remember/learn all of the best replies to various openings?
There are usually several good moves in a given position so the task is just to figure out one of them. Usually a good idea is to try to control the center with at least one pawn (two if your opponent lets you), develop your minor pieces (preferably so that they help in controlling the center) and castle. You should avoid moving a piece twice before you've developed (almost) all pieces, though obviously if you can capture a piece, your piece is attacked or you need the piece to defend something, you should move it twice.
Danny Rensch has written an article on opening principles: https://www.chess.com/article/view/the-principles-of-the-opening, if you follow those ideas, you will have a good enough position after the opening. Actual opening lines start to matter a bit later, but choosing lines is a matter of personal preference.
As a new player, I haven't even seen the half of the viable openings in this game. Because of that, it's difficult for me to remember every excellent reply to every opening. I look like an idiot coming close to aborting the game to google the best counter to an opening lol. Can anyone help out?
Don't bother. Most of them won't come up. Of those that come up there are multiple answers, and even when you get it wrong there's not guarantee your opponent will be able to follow through, etc. It's just not where your games are won/lost.
1. You should properly learn the opening principle first
2. learn a simple opening for white(for example, Queen's Gambit, Scotch Game, 4knight game, Danish Gambit) and remember the first 3 to 5 moves of the opening that you choose.
3. play 1...e5 against 1.e4 or play the Scandinavian Defense (can't think of any easier and better opening for a beginner) which is

1. You should properly learn the opening principle first
2. learn a simple opening for white(for example, Queen's Gambit, Scotch Game, 4knight game, Danish Gambit) and remember the first 3 to 5 moves of the opening that you choose.
3. play 1...e5 against 1.e4 or play the Scandinavian Defense (can't think of any easier and better opening for a beginner) which is
I was with you until number 2. That cardinal sin word. Remember. DO NOT REMEMBER! DO NOT MEMORIZE!
You need to UNDERSTAND the moves. The reasoning behind them. This way, you do not whine and bi*ch how you lost because White (if you are black) went out of book. You should understand why the moves are made so you can figure out why other moves are bad.
For example, being the French guru that I am, I understand the French, not memorize it!
Case in point:
1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6.
White now has:
6.a3 - Best! Why?
6.Be2 - Slightly dubious, but not horrible
6.Bd3 - Again slightly dubious, but not refuted
Why is 6.b3 bad?
If all you did is memorize the 3 lines, you will fail.
6.a3 is to play 7.b4 and get the Bishop to b2 to protect the d-pawn. Black is ready to play Nge7 or Nh6 and Nf5 (all this after a trade on d4 if 6.Be2, immediately if 6.a3).
If White plays 6.Be2, then 6...Bd7 is bad as is 6...cxd4 7.cxd4 Bd7 as it gives White time to castle and save the d-pawn. After 6.Be2 cxd4 7.cxd4 Nh6 8.O-O? Nf5, it is advantage Black, hence 6.a3 Nh6 7.b4 cxd4 8.cxd4 Nf5 9.Bb2!
6.b3 is horrible as it severely weakens the dark squares on the queenside. Your light squares in the center are weak. Black has too many entries of attack as it is easier for him to get to d4 than it is White to get to e6.
Memorization and Remembering moves gets you nowhere. You must try to UNDERSTAND every move, BOTH BLACK AND WHITE! Regardless whether you are playing it from one side, the other, or both.
As a new player, I haven't even seen the half of the viable openings in this game. Because of that, it's difficult for me to remember every excellent reply to every opening. I look like an idiot coming close to aborting the game to google the best counter to an opening lol. Can anyone help out?