Thanks guys for your input!
I think I got pretty ambitious with my estimate of riding 10 miles daily. My original plan was to try to ride to and from the college I'm currently attending over the summer (5 miles there, 5 miles home), but I don't think I'm quite ready for that yet. Realistically, I'll be riding 2 or 3 miles daily once I transfer to a university in the fall, so I don't need an expensive bike with the best specs.
I really do like the look of older bikes. I like the idea of improving on/maintaining a bike with a steel frame. I'm willing to put money into a bike if my funds allow it (however since I'm a college student, my budget is limited at the moment). Something about steel just calls to me.
I'm a short person at a little over 5'2. I feel like it'd be easy to find a modern frame small enough to suit me. However, the 1985 Trek 500 seems to be fit frame-wise at 48cm given my proportions. Though I haven't been able to check the fit in person. It's a beautiful bike. I worry that I won't come across another one of this size at the price it's going for.