Randerolf, if I'm one of the "fools", I'm going to take that personally.
After all, this is my job, boring as it is at times.
USAA is limited to military personnel and their families. I have USAA as well, but only because my father was in the Army. One of their underwriting secrets is limiting their customer pool to a very known quantity. That, however, is a completely different discussion.
If you are moving out into your own apartment, you also need renters insurance, which would pick up the contents of your place as well as provide you with some liability coverage should somone slip and fall there (for instance). As you can see from the other thread, No_Soup found that combining the two actually made the auto insurance much cheaper. I've had different results.
One thing I have to wonder about is the college comment that you made. If you are off to college, most policies will cover that change automatically. You should check since it might mean that you don't have to do anything.
If the car is titled in your mother's name and she's paying the insurance, you don't need to make any change at all. Auto insurance follows the vehicle, not the driver, so if someone borrows the car and bangs it up, it is covered. I trust that answers your side question?
The question about what limits you should buy is a lot tougher and that's why I saved it for last. I think that I need to caution anyone else that if they give any advice on this specific subject, they probably should have an insurance license in whatever state they're in. It's probably illegal otherwise. With that said:
Buy the highest limits you can afford. If that's the state mandatory (most are $20k/$40k/$10k), so be it. However, if you're looking for the minimum that I think is realistic in today's legal environment and with the inflation since the minimums were set over 20 years ago (in most cases), then the answer is $100k/$300k/$50k. Let me know if you don't know what those limits mean, and I can interpret for you, but if you're shopping, you should have already seen it. Personally, I think that everyone should have at least $1M, but that's my personal opinion and not my professional one.
One other thing, talking to your parents' agent is a fantastic idea. The online things are ok if you've got some experience, but having a real person to ask questions of and get opinions from is definitely worth it. Independent agents can almost always give you multiple options as well.
Let me know if I can be of any further service.