I'm right in the middle of the Amateur TT cup. It's kind of funny.
I bought a TT and ran the Beginners level totally stock, including tires (except oil change). I did not sweep the series, but I won the championship on points before retiring. I left my original TT bone stock, and I took the prize TT back with oil change, super slicks, VCD, and Lightweight 1 and 2. I beat the remaining two races pretty comfortably.
Now, I've moved on to the Amateur level. I took the lightened TT and added port/polish, sport intercooler, and chip. That's been enough for the first three races but I think I'm going to need more for the later two.
I should have gone with the racing intercooler for more top end HP. I'm also still on the stock turbo setup, which I may have to upgrade to T1 or T2. So far I've only been able to win by qualifying on the pole (barely), and grabbing a small 1-1.5 second lead at the green. If I run three perfect laps, I'm enough faster through the twisties that I can hang onto that lead despite the huge HP disadvantage I seem to have. If they get close to me, they can blow by like an express train on the longer straights. They have to be running a T2 upgrade to be pushing that much HP up high.
I have done no suspension work at all, because I don't seem to have any handling problems after cutting the front torque down to 30% with the VCD. That may change after I add power.
Good luck, and hope this helps!