I'm in Missoula and I have
trees and plants for sale:
https://mountaintimefarm.com/
If you're looking for affordable building materials, Waste Less Works
https://wastelessworks.com/ and Heritage Timber
https://www.heritagetimbermt.com/ are great places to get materials. Home Resource used to be great a place to get used stuff, but it got taken over by this really manipulative cruel psychopath lady, and so people are sort of boycotting that place until she's gone, and I'd recommend you do the same.
For fencing, you will need 8' tall to keep the
deer out, and then plants will just sort of start magically appearing all by themselves ("fencing for one year is like planting for ten"). There are a ton of places that
sell fencing supplies up and down the Bitterroot and in Missoula, and they're all priced about the same, but it's usually worth calling around to check prices and availability.
For IDing unknown plants, this book works pretty good: Vascular Plants of West-Central Montana
https://www.fs.fed.us/rm/pubs_int/int_gtr277.pdf
For info about plants you've identified:
http://montana.plant-life.org/
Also craigslist and
facebook marketplace are pretty handy for acquiring and/or disposing of things.
For anything else you need, this forum is a great place to ask.