I would definitely use the college facilities. There are probably people of all levels there and most times people are much more concerned with their own workout than they are with yours. I had some trepidation myself before I joined the gym in Nov and I was amazed at all the regular looking people there LOL I thought they would all be your typical hardbodies. Everyone at my gym pretty much just does there own workout and is living in their IPOD worlds
There definitely is gym etiquette like don't hog the machines or weight benches by just sitting there or leave all your junk around for people to trip over. Wipe off any machine you use with a paper towel. They usually have spray bottles and paper towels for that. Noone wants to use sweaty equipment.
As for how much exercise and how often, I would if you have the time try to work each muscle group twice a week. There are lots of ways to divide it but for example I do upper body on Tues and Sat, lower body and core Wed and Sun. That should take about 30-45 min per session. For cardio you can get a lot of extra in just by parking further away or walking to all your classes, using stairs etc I would try to get in around 30 min a day and if you can manage 45 that would be good. Whatever aerobic activity you like swimming, biking, walking , running just make sure you feel the effort, are a little bit winded. You can check your pulse etc to make sure you're in a good aerobic zone.
For diet drinking water is a good idea, switching to diet pop is definitely preferable.
If you go to Wendys your best bets are the single hamburger (420 calories no cheese) or grilled chicken (370 calories) If you get the small fries that another 440 (large fries are 590) but better to opt for the side salad (140). The other salads are pretty high (caesar salad 540, taco salad 710, chicken blt 780, mandarin chicken 580). The potatoes are ok (baked potato with sour cream 320, broccoli potato 330, bacon and cheese 440) or chili (small 220, large 330) Frescata ckub 440, or turkey pesto 420 are the best for cold sandwichers. If you go to Wendy's it better for lunch so you have time to work off some of those calories and compensate with a light dinner.