Seriously. You're making a huge deal out of something simple.

7.5 miles? You can ride anything. Get a $300 rigid mountain bike, slap some fenders, lights, smooth but fat tires and a rack on it and you have a perfectly capable road and off-road commuter for under $500. Forget hydro brakes, ridiculous overkill, you're not racing downhill at 50mph. Low end mechanical Hayes disc brakes will send you flying over handlebars.