Hi Gina! I am actually from Eugene and starting at NAU in the fall for the full time CDS track. I'm currently at UO but have been to Flagstaff lots of times both on campus and off and I love it! It's a great town, has a pretty similar vibe to Eugene if you ask me (I'm assuming that comparison might be helpful since you're from Portland haha). It will probably be an adjustment from Portland but everyone has always been really friendly to me there and there and I am really excited to move there in August. My oldest sibling went to undergrad there and she says it's a very student friendly town, and yes to the question about being bike friendly but I'm not super sure about public transit.
Hope any of that helps and I guess I will be seeing you in the August!