I read at the rules "the controls schema should be the same as the gameboy's"...

Then, for keyboard controls can I use [space] as A button and [esc] as B button for example? Or I should use a given convention?

I'm not part of the committee running the jam, but why not just use [Z] for "A" and [X] for "B"? It's fairy common for GB and NES games and works rather well. Is there a reason that space and esc would be more useful options?

Yes, I also though on a ZX scheme...

You are allowed to bind your keyboard however you like. I have seen concerns raised over using the Z key however, as some keyboards will ignore the Z key depending on the number of other keyboard inputs currently given, and also the AZERTY users will have it significantly displaced.

I finally don't submitted the game, but the jam schedule helped me to make a base for a game. Thank you, I appreciate the comments