How many openings do you have in your main repertoire?

We've all heard that beginners should stick to the same openings. Also as adult improvers, we have limited time for chess study, learning new openings could be too painful for some of us.

But we all want to be cool like top GMs who can switch between e4 and d5 or even a4! with ease.lol.

Do you usually play more than one opening each for white and black (against 1d4 and e4)? How well do you know the theory of those openings?

For me, I play 1d4 as white; generally Queen's Gambit if black allows it, but also face lots of KID, Benoni and other offbeat openings that black can choose.

As black, when face against 1e4 I play Caro-Kann, and against 1d4 I play Benko Gambit.

I feel like I still can't memorize all of the lines in those openings especially the sideline ones. So learning new openings seems like it would be too much for me to handle, even though I might one day.

You should not memorize, but understand. An opening repertoire grows slowly but steady over the years. You start with your mains and stick to them because you know them so well. Then sometimes they need a repair, and you learn a backup.

I have two serious White opening moves: 1.d4 (main) and 1.c4 (solid). After 1.d4 d5 I play 2.c4 (main now) or 2.Nf3 (old main). After 1.d4 Nf6 I mainly play 2.Bg5 or 2.Nf3.

Sometimes I also play 1.e4 and 1.f4 (or 1.b3) for fun, so I have a small repertoire here as well.

Against 1.e4 I play 1...c6 (main) or 1...Nf6. My main weapon against 1.d4 (and 1.c4 or 1.Nf3) is 1...f5, but sometimes I play 1...Nf6 and after 2.c4 I can play 2...c5, 2...e6 or 2..d5.

As White I play 1.Nf3, then transpose depending on what Black plays. My most common transpositions are: English, Nimzo-Larsen, QG, and occasionally KIA.

As Black, I play Sicilian against e4, mostly.

As Black against c4/d4, I'll play either NID/Bogo, or QGD.

Regarding theory: I don't really know or study proper theory - nor do I care to. Mostly I just focus on certain setups or variations that I prefer, and I try to steer the game into those waters that I'm most comfortable with.

I analyze each game with an engine afterward, to see if I missed anything crucial, or to see if I made some fatal mistakes along the way.

My repertoire is larger than it needs to be simply because it will always be larger than my opponents' repertoires.
As White:
I play everything solid on offer in the 1. e4 e5 complex barring the Scotch and even that may change soon because the positions arising after 1. e4 e5 2. Nf3 Nc5 3. d4 exd4 4. Bc4 are exciting to me what with 4... Bc5, 4... Bb4, and 4... Nf6, each with their own plans and ideas and tactical complications, and I already know all the ideas as Black from the mainline Scotch defenses (those being the Malaniuk, Classical Intermezzo, Schmidt with 8... Ba6 or 8... Nb6, and the Four Knights Scotch with 5... Bb4 and the forcing line that follows).
I play the Open (against 2... e6 and 2... d6), Rossolimo (against 2... Nc6), and Delayed Alapin (against 2... d6) Sicilians.
In the French, I play the Classical and Poisoned Pawn Winawer, the Alekhine-Chatard Attack, the Boleslavsky Steinitz, the Morozevich Burn, the Lasker MacCutcheon, the Chigorin MacCutcheon.
In the Caro-Kann I am a simple man. I play the Endgame Offer Caro-Kann (thank goodness it finally has a name), because I've played everything the Caro-Kann has to offer and I just don't like the positions that arise without the early queen trade or some form of gambit like the Toikkanen or the 2. Nf3 3. d3 4. Ng5 tricks with a good position down a pawn if declined.
Against anything else, I either know the mainline or the refutation.
I ALSO play 1. d4 complexes such as the Catalan, the Meran and Botvinnik Semi-Slav, various QGD lines, various Slav lines, the QGA lines, the Tarrasch and Semi-Tarrasch lines, the Kmoch and Classical NID, the Kasparov-Petrosian, Traditional Mainline, and Anti-QID, the Taimanov Benoni, the Mar del Plata KID, the Hungarian Russian Grunfeld, the Alekhine Anti-Grunfeld, the Saemisch KID, the Goglidze Neo-Grunfeld, the Modern Benko Accepted, the Mainline Benko Declined, the Duz-Khotimirsky Blumenfeld Gambit and Blumenfeld Accepted, and I'm sure a bunch of other lines I've forgotten here. 
As Black, I'm a little simpler. 
Against 1. Nf3, I play 1... d5, either the Reti Gambit, some Reversed KID/Grunfeld, or a 1. d4 transposition.
Against 1. c4, I play 1. e5, either the Four Knights lines or Keres Two Knights.
Against 1. d4, I play the Slav, Ragozin, NID, and Catalan/Retreat BID.
Against 1. e4, I play the Sveshnikov, Anti-Sveshnikov, Rossolimo, Closed, and Barmen Alapin, as well as 1... e5 with the Neo-Arkhangelsk and Berlin Ruy Lopez, Two Knights Italian and Giuoco Piano Mainline, Schmidt Scotch with 8... Ba6, Four Knights Scotch/Spanish/Italian, Falkbeer Vienna Gambit with 5... Nc6 and the queen trade, Frankenstein-Dracula Vienna, 3... Bc5 Mieses Vienna, Bishop's Opening with 2... Nf6 and 3... c6.

I'm a club player.. and not all that interested in modern mainlines. As White, I have two opening lines then branch out from there.

1.d4 2.Nf3 & 3.e3... with the idea of playing the Colle Koltanowski, or transposing to Queen's Gambit, QID, KID Chigorin, Slav etc.

Then...

1.d4 2. e3 3. Bd3.... with the idea of playing the Stonewall Attack, or Queen's Gambit, or a reversed Queen's Gambit of some sort, or a QID, KID, etc.

Not the most optimum opening repitoure, but I get to draw from a lot of cool ideas from bygone eras, played by extremely talented players.

SO FAR....what I've discovered is "usually" my opponent's don't know the finer points of the lines i play ... (I assume it's because they are focused on the latest and greatest of the modern era)

As I am aging, I am shrinking mine.

White - Trompowsky (Against 1...Nf6), Levitsky (Against 1...d5), 2.Bg5 Dutch (Against 1...f5), French (Against 1...e6), Exchange Slav (Against 1...c6), Modern (2.e4 against 1...g6), KID and Old Indian (1...d6 2.e4 Nf6 3.f3 and now 3...e5 4.d5 or 3...g6 4.c4)

Black - Petroff, Dutch (Via 1...e6 and 2...f5), French (Via 1.d4 e6 2.e4)

I can tell that you're quite passionate about openings. lol.

Your opening knowledge is remarkable! As a QG player, I can relate to most of the 1.d4 lines that you mentioned. Funny enough, I just finished a Grunfeld game, totally exhausted! haha

Can you share a Trompowsky player's secret? lol. Which line do find the most troublesome for white?

I've always find that white always has an easy game after 2.e6 or d5. I haven't tried Ne4 yet though.

I'd probably have to say 2...c5.

I never could get a handle on the Dutch. I tried a few times, but got blown out the water ... It's certainly a tricky defense to handle well.

Yeah, I agree. It's a double edged opening; very aggressive but leaving your king a bit exposed on light square diagonal.