I would do a separate fuel system for the NOS and use VP110 in a little separate fuel cell. You can see how I did mine somewhere in this thread. 91 in the main tank is fine. That is how I have mine now.
In the instructions they recommend a separate fuel system. There is a loop wire in the EFI system that gets hooked to the NOS Trigger wire that will fine tune the A/F Ratio on the NOS Hit using the Injectors. You set the Target A/F Ratio on the NOS Hit in the set up screens. Pretty cool feature.