If you are going to get a card, get one with a stupid low limit, like $500, so it can't get out of control. If you can get a 0% card for any amount of time, that's great, but at a young age with limited/no credit history, look at the fine print and make sure there aren't any fees or any other bullshit charges, like for non use or a yearly fee or anything like that.
And as for building credit - the rules of the game aren't what they were. They want to throw cards at anyone that will take them, and are cranking up everyone's rates, regardless of how good their credit is. I'm to the point where I'd like to get a fixed loan to pay off my CC and my student loan just so I have a single payment, and know what it will be every month without having to worry about the next month's payment being way more for no reason. And I've got a zero percent card, too.
I hate to say this, but you may also want to think about a change in priorities. Considering you are trying to work and go to school and what not, it may be best to get down to one vehicle that's reliable, whether its the mustang (and not mod it) or something else that's cheaper to keep on the road. Sometimes a newer vehicle with payments is a better idea than a car you paid cash for, but needs a $200 - $500 part every month, as downtime can cost you too. It's hard to argue with some of the new car warranties out there these days.