What Does It Take To Support F.I?

Rally

Hey everybody, I just got my gismo (Apple Spellcheck )and I want to put a GTM TT in it.
But I have a few questions, the biggest and by far most important is just what other mods will I need to add to the car to support the TT?
Second question is a lot off topic but what are the best (And reasonably priced) coil overs?
3. What are the differences in the GTM TT stages? Like the 500hp vs 1000hp one? Are those the numbers on what the kit is capable of? Or are they the HP you will get with it? Sorry I'm not very knowledgable in car/engines.
4. This will prove how dumb I am when it comes too cars. So if I get a g3 stillen intake, and then install the TT kit the next week. Will the g3 intake still be of use? I guess what I am asking is does the turn key TT kit come with an intake?
5. (Warning: Another beginner question) If I get the Fast Intentions exhaust do I still need to buy a high flow cat? Or is that included in the F.I exhaust? Sorry for all the questions but if someone can just answer one or two of them and another person answers 1 or 2 it would be great! Thanks everyone, and I appreciate all the help and will give rep!