My 3 cents:

I think it would be nicer if you would split the board into dire (Scourge) and radiant (sentinel) instead of black and white.

Then for the heroes, use according to radiant or dire heroes as well. Can refer to this:
Radiant: http://dota2.gamepedia.com/Radiant
Dire: http://dota2.gamepedia.com/Dire

If you have the time to build the pieces, I would suggest to build every pawn with a different hero. Then you can differentiate them by sizes between pawn and the other pieces.

Knight can go to those heroes with a mount.

Others, still need more brainstorming

Cause plain creeps for pawns is boring?

So rather you differentiate the pieces on front row vs back row by sizes