All good advice here. I'll add that if you're buying it from an individual MAKE SURE THEY HAVE THE TITLE. There are a ton of bikes out there where the owner lost the title or the bike is stolen and there's no title. So no real chain of ownership.

Also, personal advice rather than second hand buying advice, taking the course qualifies you to drive in a parking lot (it's a good course, no hate from me). Don't go big for your first bike. Get a smaller one and toodle around until you're comfortable.