Are 64bit primary domain controller and 32 bit additional domain controller possible?

Yes, but the Win Server OSs that comes as32bit (X86) are Win2008 RTM and older.

Sure , go start to do it now with no any problems

Of course its possible....

Possible but not recommended. Keep in mind the era of32 bit computing is ending soon. Even majority of client side OS are64 bit now. I would not recommend doing it at all unless you have a sold reason to do so.

YES its possible all the thing you have to do configure domain functional level. Hope answer the question :-) .