Welcome to amateur radio, sigxbill - and welcome to one of my favorite parts of the hobby! I build repeaters, too, since the 80s and I haven't gotten bored with it yet.
Although coordination is "optional," a responsible repeater owner is a good neighbor who goes through the process.
A repeater - especially one that has very good coverage - is a big investment. A large repeater system may have tens of thousands of dollars invested in it. I guarantee that a coordinated repeater owner will not be happy with someone setting up within range on the frequency pair they are coordinated to - to the extent of potential litigation (yes, some people take it that seriously). My advice (which is worth as much as it costs): Do it right, or don't do it.
That said, many coordinators have what's called a developmental pair. That's a place where you can set something up to see if it works for your purposes, and then you can migrate it to a permanent assignment once you are sure it suits your needs. And, repeaters are not as popular today as they were 25 years ago. Coordinated spectrum is more than likely available and readily obtained in many areas of the U.S.
About your prospective site and system implementation, I doubt you'll have coverage beyond the peaks. There is some "diffraction" over sharp objects, but that's not usually a reliable mode of communication. You might find 6 meters to be a band that might work, although 6 meter portable radios aren't as efficient as 440 ones would be.
I'm guessing that doesn't matter as much as experimenting and learning. By all means, do it! You'll learn a lot, all of it can port into earning money as a technician, and you have room to scale things up or back as your interest and capabilities carry you. But take the effort to work within the framework that's out there. That puts you on the same par as all of the other repeater owners.
I'd also like to draw your attention to a great website where you will learn a great deal:
Welcome to Repeater Builder Dot Com You've probably been there, but if you haven't, there are volumes there about how to build a repeater from radios to antennas and everything in between.