You most likely can't roll back to Nougat once you upgrade to Oreo without the aid of external software on your PC (namely Odin) and flashing your phone with the firmware you want.
I've flashed on phones prior to my note 8 without any problems but haven't done so with my Note 8 yet so can't say how easy or difficult it'd be.
As for bugs and whatnot, after updating my system, has been pretty solid, colours slightly more vivid, slightly more responsive,
Things that kind of annoy me is the persistent notification when somethings running in the background. The concept of it is good - to let us know if something is running without our knowledge but the execution of it, not being able to dismiss it for items you choose to (or at least as far as I can tell) is annoying.
Can't speak about the battery at the moment but it looks like it's similar with what i had on Nouget.