1. There are mods, but if you really want to go fast, get an SRT6.
2. Parts availability is limited.
3. Routine maintainance is a bit more expensive than your average car, but not too bad, really.
4. I've had no problems at all in over 3 years.
5. I would have a rental examined before buying it. While some rentals, no doubt, have been abused, I would suspect that most were driven reasonably.
6. This is really a great car, that I and others enjoy greatly.
Wish you well in your decision.