My basement is getting done and there is not quite enough room to frame in the prehung door where I want it cause of ducts. I would have to remove like an inch off the bottom at most. Is this ok to do? And what is the best way to do it?

Hi all I'm guessing this is a frequently asked question; sorry if it's a repeat. I looked back a few pages of posts, but didn't find anything addressing my question: I'm looking to replace two external doors, one single-width window, and two double-width windows. These all leak quite a bit and aren't very attractive. So far, I've found varying bits of information about this process, and wide differences in prices. I'm feeling a bit overwhelmed right now. What should I be looking for? Is there a "beginner's guide to contracting window and door work" somewhere that can give me a starting point? Thanks