1. I'm not sure if the S and RS seats are the same. I think the RS seats get larger/tighter bolsters.
2. It's a regular wet sump
3. Yes, there are bushing kits available that increase caster that are supposed to also increase steering feel. Superpro makes one and Whiteline does also.
4. There are a couple of options for rear swaybars and increasing spring rates should also achieve the same goal. Uprated haldex controller probably isn't going to do too much since the RS already has a sport controller.
5. The 2.5T does run hot but I've never seen any issues with overheating the motor on the track, and that includes lots of feedback from folks that go to the Ring. The brakes do suffer from overheating and there are a number of ways to address that (pads, fluid, RS4 calipers and rotors all the way up to C7 RS6 390mm rotors).
6. No changes announced or expected.