> It would cost $900 to repair at the dealership.

Unless the car is under warranty, and you're going in for a covered repair, you don't take it to the dealership if you can avoid it.

Anyway, everything you have mentioned here is relatively inexpensive to fix, and tires are a "wear item" that you'll eventually have to replace on ANY car.

I would keep driving it until you have an ACTUAL problem with it, like the engine issue that you mentioned. The car shaking when you go over 80mph is likely because you need an alignment, which again, is something you'll need to do periodically on any car.