Coleman is now starting to be more realistic about how much room each person needs. Their formula used to be 1 person = 2x6 feet. I have no idea how they came up with that idea since nearly all of their sleeping bags are at least 30 inches wide. They seem to be getting better now though. I have never had an issue with Coleman tents. If they are kept clean and allowed to dry before storage they should last for years.
For the OP, I would say that 9x10 should work well for you. Before you buy I would check out a Gander Mountain, Cabela's, Dicks, etc. Sometimes they have some really nice deals on tents and you can get a lighter higher quality tent for a reasonable price.
I would suggest using two tents. One to sleep in and one to keep your gear/clothes/etc in. Your car could work for this as well. Another tip, get a small rubbermaid tote to put your shoes in and keep them outside your tent. They will stay dry and your tent will stay cleaner and smell better.