Hey Slaughter,
As one who's fallen in love with the short Plains-style bows I'd definitely recommend making a few longer bows first. You can get away with a lot of mistakes, relatively speaking, in a 65-70 inch bow. You can't get away with anything in a reletively narrow-limbed 45 incher, even if you back it. That wood's under tremendous strain.
It might be worthwhile to start looking for a nice osage, black locust, white oak, elm or mulberry stave for your short bow now, so that when you feel like you're ready for it you'll have a nice piece of wood handy and dry. I'm working on a 48 inch osage Plains-style bow as we speak and I'll post a few pics once it's done.
All the best,
-Eric