dont use any of the plastic covered acorn nuts, the second it rusts a little bit you wont be able to remove it again
and remeber that mixing steel and stainless steel means that anyplace the 2 materials are in direct contact, the steel will be sacrificed to the rust. a SS nut will be stuck on a steel bolt just like a steel nut would get stuck to the same bolt
all SS hardware or no SS hardware is the way it should be done, and even then you want to insulate the SS hardware from any steel pieces they may touch by using plastic or rubber washers to insulate the different metals from each other
(IE: ss bolts & washers holding steel panels together, with plastic washers between the steel panels and the SS washers)