I have a Thule rack that bought used, and have moved between several cars. Any time you buy one of the racks you have to get a fit kit with it. For my Thule, and I bet it's the same for a Yakima, that consists of the pad part that actually rests on the roof of the car, and the clamp part that fits in the door. So you just have to get that after you find a rack. For example here's the Thule fit kits, with Yakima they are called Q Clips. I always just googled to find the one I needed. Ebay is a decent source for the fit kits too.

The only thing about the rack itself that you need to worry about is the bar length. Are the bars long enough to stretch across the roof of your car? They can definitely be longer but you don't want to put stuff way out on the ends if they are to long. You could put a single bike mount on the outside of the towers though safely.

Other than length just look for one with the mounts you want. Don't worry about what car it came off of.

I have left my mountain bike locked on my rack, but generally don't like to. I wouldn't leave it there all day at work if I was planning a ride immediately after, but would leave it while I ran into the grocery store to grab some drinks for the ride.

Hope that helps a bit.