Go for it! You'd be crazy not to!
I use an Epson V700 for scanning my 645n negs. I found that the stock Epson film holders aren't very good, so I bought Doug Fisher's aftermarket 120 holder plus a piece of anti-Newton's rings glass. After considerable fiddling I can get scans sharp corner to corner. Of course if you can find a good service they could scan for you, but if you shoot a lot your own scanner might be a good idea.
As I recall the "plain" 645 gives 15 exposures per roll of 120, the 645n and 645nii give 16. Mike Butkus' wonderful Orphan Camera site will furnish an instruction manual
Pentax 645 instruction manual, user manual, free PFD camera manuals I've found KEH a reliable source of used gear for the 645.
As others have suggested Freestyle is a good source for film. apug.org/ is an excellent forum for film users.
Processing is a problem. BW is easy at home, although loading 120 film into a daylight tank I find more difficult than loading 35mm. C41 I am told is no more difficult, but temperature control is critical. I'm in the Atlanta area and we have at last a shop in Dunwoody which looks promising since other good labs have closed. I've got some Velvia 50 to shoot in the mountains next week. Since I scored a basic Kindermann projector I hope to enjoy slides, which I haven't done in years....
Buy a good tripod, Manfrotto or such. Given your profile you probably already have one. Folks here on the Forum can offer valuable advice. An extra film insert or two is a really good idea! Its no fun reloading that bad boy in the field with no shade available. The ones marked 220 are usually cheaper and can be converted to 120 with a tiny screwdriver, care and manual dexterity, and about two minutes time. Somewhere on the Forum there's a discussion of the process.