What to play after 1.d4 for beginners.

King's Indian Defense is an advanced opening, with a lot of theory to learn and understand if you expect to play it well. 

Against the Queen's Gambit (1.d4 d5 2.c4), a better choice, and easier to learn for less advanced players would be the Queen's Gambit Accepted (QGA); also give the Albin Counter Gambit a look.  You might also check out the Stonewall Dutch Defense, another playable defense, effective against 1. d4 in general.

Nimzo Indian

(and don't give White the space, fight for the space).

* But you should know - he can transpose to a Catalan, so you should know how to play Catalan as Black - be solid - don't take the pawn.

I suggest, instead of Caro Kann, play 1...e5:

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If he plays 2.Nf3, play 2...Nf6 - Petrov / Russian - now it's Your opening, White only responds to it. and you have a Stafford Gambit if your opponent is gullible. (watch an Eric Rosen video)

(if you'll play the Objectively correct move - Nc6, you'll need to be ready for... Ruy Lopez, Italian game, Scotch Game, Four Knights, and all of their variations, plus dozens of gambits).

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If he plays 2.f4, play 2...d4 and have a good time with the Falkbeer Countergambit.

https://en.wikipedia.org/wiki/King%27s_Gambit,_Falkbeer_Countergambit

(the old line is refuted, so just play the Nimzovich line).

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if he plays 2.d4... - the center game...I'm not good at that, but: he didn't play a good move, you'll need to learn a little:

https://en.wikipedia.org/wiki/Center_Game

(If he tries the Danish Gambit - c3, just play d5 - refuting it on the spot).

In general you can try and play almost whatever defense you like. It is true that KID is more difficult for novice players, but you will be playing against novice players yourself. 

All that being said, it is probably more straightforward to play 1. ... d5 just because you get used to controlling the center with pawns (classical approach) and go for either QGD or Slav/Semi Slav defense. Play that for a few months at least, try to follow opening principles and then decide if you wish to stick with that or you want to switch up. Now is that the only way? Of course not, but it is probably the most straightforward approach for a new player.

You can also play 1...e6 - the French Defense, it's really hard for White players, I speak from experience. Your game is easy, and you usually don't castle to the kingside - it's a mistake. and yes, your light bishop is stuck, unless you play a French Defense which breaks the pawn chain - e.g. Rubinstein variation...

Easy game:

https://www.youtube.com/watch?v=mMivcJQkGw8

It's hard for White because you can choose a variation in a later part of the opening, so White needs to be prepared for all of the variations... unless he plays the Advanced French - in which your game is Super easy I believe.

1. ...e6 after d4 is not a French defense though. It could transpose if white plays 2.e4, but those who play 1.d4 will probably more often than not play 2.c4 and go into QGD instead.

1. ...e6 gives white more options. It is ok for someone who plays French against e4.

PS: Go Crag Hack.

People who play the Exchange French and the London are boring. They need to get a life. 

you should watch gothamchess

As a player who was quite recently at their level (And your level), they're right

All of the thematic pawn breaks, knight maneuvers (nh5 to go f5, a5 + na6 to go nc5, e5 and f5 pawn breaks, thematic c5 break for white in Bayonet attack, Benoni transpositions and weaknesses on d6 etc etc etc) is just way too much for a person of their level to keep track of. What's going to happen is that they'll start messing up move orders, let their center and pawn structure shatter and then end up with a naked king facing a wall of white pieces on the kingside