1) 2d4 d5 3Nc3/Nd2 is strongest for white and imo the only way to get a very small theoretical advantage.
2d4 d5 3e5 is unclear and still developing, black shouldn´t be worse but the systems are not worked out
everything else serves no real problems for black, I cannot understand the popularity of phantasy var
(weakening the kingside) or exchange var (getting a worse ending). And the only problem for black
in the panov is that while black wins d4pawn white may liquidate queenside pawns and reach a drawish
3-4 rook ending.
2) yes, in practical play KIA setup is sometimes annoying if white knows how to play it well.
the same for advance Short system if white knows how to play it dynamically with a well-timed c2-c4
(most white player below master level don´t know)
I would recommend to play the main lines with 3Nc3, it´s some work but it pays off. You have to deal with many different subsystems but in the 2knights this would happen too (where black has many options: 3...Bg4(Bxf3,Bh5), 3...dxe4 (Bf5,Bg4,Nd7,Nf6), 3...g6, 3...a6, 3...h6, 3...Nf6).
If you work on your repertoire be aware that after 1e4 c6 black is not committed to 2...d5 !
Especially 2...g6 is playable but there are also 2.c4 e5, 2Nf3 d6, 2d3 Na6 and similiar things.
And, the best way to study the Caro-Kann is to play it with Black!!
tracke