Alot to consider for hardwoods but here's my take...
Better make sure your subfloor is suitable or you will run into another wammy. You can't get a straight answer across the board for everybody has their preferences and so many variables, but I prefer 7/8" total (nothing compressed or particle / all pure ply) by means of 1/2" under 3/8" with the 1/2" laid longways on the floor joists and the 3/8" all laid at 45 degrees with the 3/8" screwed with 5/8" screws at no less than every 16".
I prefer cleats and NOT staples for various reasons.
All the door trim and corner round has to come up so there's a HUGE cost considering re-install. Trim can break and damage easily so if you pay someone, hands down supply all new trim...
I prefer unfinished not the prefinished crap. You have a smooth surface to sweep / mop / smop / dust and it seals way better. Actually prefinished does not seal period...
Any layman can do the job with good knowledge but once it's laid, it's there and you will have to live with your mistakes. I can go back and show you every detail where I messed up on the floors I've done although I'm usually the only one that can notice without pointing it out.
there's a HUGE toll on the body if not used to this work. It works every muscle.
After my 5'th, I think I have it down to a science but I don't do side work any more. I only give out advise...