Shoes--wear what's comfortable. Lots of people wear crocs and if they work for you, then great! I usually wear whichever pair of running shoes I've just demoted, LOL. You're going to want shoes that are supportive, definitely.
Diet: Don't do anything drastic
Substitute healthy foods for non-healthy ones. Avoid white sugar as much as possible. I'd shoot for eating better than losing weight at this point; I bet weight loss will follow, but you don't need the stress of a low-cal diet now.
Socks: comfy ones that fit in your shoes
Exercise: Walk 5-7 days a week. That will build up your leg muscles as well as your abs to an extent without being too hard on your body. That's great you have a treadmill at home. Buy some hand weights and do a few tri/bi/shoulder reps 3 days a week. Those won't take much time, but you should notice a difference in a few weeks--you'll be stronger and your arms will be cuter
Increasing energy: SLEEP! Seriously, hard as it is, try to get enough. It will help immensely in work and school. Learning new things takes a tremendous amount of energy (at least it does for me) and since you're in for the long-haul, caffeine only goes so far. Whole grains, fruits, that kind of food will help pace you through your day. Drink enough water.
And have fun! You'll have a blast and when it's over you won't believe how quickly it went.