The move I'm curious about here is 2.d3. Why block in the light squared bishop when there is no need to, and the e4 pawn is not under attack?

That's the Indian attack. A reasonable choice for some

Unfortunately, they can also be trapped. Like here, if black plays c6. Later the text mentions that white voluntarily loses the knight, but he has no choice in the matter.

yup, d6 and the knight is toast.

no, c6

At any rate 4.Ne2 was indicated - quite in keeping with a King's Indian Attack.

Do u mean u don't mind exchanging your Bishop for your opponents Knight, or vice versa? because Bishops are generally better in more positions than Knights, so another motivation is needed for such an exchange (gain of tempo etc..).

No he still has the advantage, c6 and that Knight is gone.

Well, after 6.Nf3 cxd5 7.cxd5 White retains a presence in the centre. The alternative was 6.Nf4 and if 6...exf4 7.Bxf4 gains something for the piece, even if owhere near enough. But the intermezzo 6...Bb4+ could be nasty, at least displacing the White King.

The d5-knight still has no moves... But I agree, Black would have been better off taking it at once instead of moving a second time his only developed piece.

... and having moved it to g4, he probably ought to have exchanged on f3, or maybe played ...Bh5. Even so, a knight is worth more than a pawn plus 2 tempi...

It can hardly be called a sacrifice, u have no choice!

The best that White can do in the circumstances. The alternate recapture loosens the centre.

The idea of attacking is good...but one knight and a passed pawn can do very little by themselves. A better plan is to develop more pieces and then attack.

Though recovering the second pawn for the missing piece is not a bad scheme. For the knight, White has 2 pawns and a big centre. Black keeps an edge, but it's not a big edge...

11...Bxd2 ought to come first into consideration, whatever the final choice. Exchanges enhance Black's material edge, and diminish the effect of White's central bind. Note that it would be White's "good" bishop that disappears (White's other B being much more encumbered by its own pawns).