Can I use the stock controller for my HZ champ for the bnf ultra micro t-28?

Yes sir you can.

Why they don't make a BNF Champ? I don't know, maybe because they are so cheap in the first place
My son has the Champ, I have just about all the PZ Micros.

will i be able to use all the functions eventhough the champ is a 3 channel controller?

Yes, because the controller is actually a 4 channel controller

I think il go with the t28 micro..