Re: irimi nage spinning
I've seen many dojo's do Iriminage Ura many different ways. I suggest asking your sensei.
The problems I have seen doing this have been:
1) Improper distance (gap between uke and nage(I prefer the "plant the uke's head to my shoulder method))
2) Timing (nage is going to fast or too slow)
3) kuzushi (Usually giving the uke back his balance right before the throw)