IM pfren, what would you play as white's third move in this situation?
You got to be joking.
If not, then it's bad for you, and your overall understanding.
ANY move that protects e4 without violating chess principles (Nc3, Nd2, Bd3) is good enough for a large advantage.
Nah, not that easy....
Black isn't obliged to cooperate that much. For example, after 1.a3 d5 2.Nf3 c5 3.c4, the move 3...e6 is perfectly good. Black should be equal in most of these lines, as long as he doesn't fix the central pawn structure.
Well equality is good enough...
And, some
If Black doens't take, then we still have it fine. Just fianchetto the King Bishop, and White should be fine.
Also, is playing 1.a3 an okay idea in OTB?
I have my first OTB tournament next week...
Any suggestions as in what to eat, how to prepare so my mind functions at its best?
times they will cooperate that much. But even if they don't, there's not much to worry about.
If Black plays e6 then...
I don't like 4... dxc4. Here's an alternate 4... that I thought up. I wonder how sound it is:
Actually, this is what White wants. White wants the center closed so that he can attack on the Queen Side. Oh wait! White can get a Reversed Benko here with +1 tempo again because here White can play b4!
And even if White doesn't, White will definitely have a fine game! As pfren said, White wants the center closed in order to attack the Queen Side.
Even the engine says -0.35 about the position after Black plays d4, which is not bad.