E85 and Nitrous go together like cookies and milk!
I would send your system out to someone like Monte or Induction Solutions to get it flowed. This gives you a good baseline and tech support that is more than worth the money you spend on the front end! Opinions and individual results always vary so having someone that knows what they're doing take actual measurements on your system gives you a known starting point. You might also be surprised at how little extra E85 you need to get a clean plug and keep the motor happy. For instance, my fogger has a 0.002" SMALLER fuel jet than the Nitrous jet with just a tick over 6psi flowing and still shows a little fuel on the plugs. YOUR RESULTS MAY VARY. My system has been flowed so I had a good baseline.
For what it's worth, a couple key things I've learned over the years:
Test at the pump and fill drums. It's consumer grade pump gas, so this at least allows you to know what % you're using and not relying on whatever % they drop off the truck that week.
E85 will pre ignite. My hoagie seems happy with a -10 heat range plug. It's only 11:1 on roughly 250hp shot.
When in doubt, pull timing out. The timeslip will tell you if it's the right move.
I'm in no way an expert. I just try to apply what the guys that are a TON faster and smarter than me are doing to my setup. So far it's allowed me to make the car run a little better every year and most importantly, not break parts.