Adam:
You need a memory card to save your progress.
There are some places that have a '2 controller' package. Some stores also have an online package where you get the cable modem adapter for a little more $$.
The only add-on I have considered is a steering wheel joystick. That said, the little hand held controllers, with practise work well in the car sim games.
Dave: as you can see, I'm also not a big fan of high hp cars - my 'modded' Miata only have 240hp! And I'm able to keep up with the other cars thrown at me!
-Z.