The RST is a great organic style clutch upgrade over the OEM one for sure. It can slip easier and take the abuse of higher RPM shifting. This ones is good to about 850hp. With your questions.
1. Yes, that is a transmissions feature and nothing to do with the clutch.
2. Yes, they still need...
I love this wheel on this platform! I run them on my 18 but here is a customers car with the bronze versions on his 24.
If you do decide to go this route, please let us know if we can help...
Headers over the years is normally a 20-30hp gain and about 20 or so ft lbs. But that isn't at peak. Most headers pending the design will see gains in the mid range while helping with torque on the lower end.
With running a GESI or GREEN cats, it won't take away from the power gains either as...
On a 30 sidewall, you will have a little more gap but it will fit nicely. Just make sure the alignment is set to the springs specs and not OEM.
When you do decide to pull the trigger, let us know if we can help as we do a lot with STEEDA! We run their springs on our shop 24 as well...
If you are looking to just do the axle back portion, the most popular brands I've been seeing is MBRP, Corsa, Borla, and ROUSH.
When you decide, let us know if we can help you on a set...