Just some ideas on the assists... I run the game on a PS5 with a Dual Sense set up to steer by turning the controller side to side. I swapped the R1 and R3 functions so now boost items are activated with R1.
I'd start with the assists all turned on and to max. They're all under the settings menu anytime you pause a race. Controller sensitivity is in the next menu, it goes from -2 to +10. Some cars will not turn to their tightest radius at lower settings. Others will turn the wheels to quickly and induce a skid or worse, send the car flying (I'm looking at YOU, Bugatti!) Remember it's there and leave it at zero. Countersteer assistance affects this also, you get tighter turns without it but you're more likely to spin out under heavy braking.
As you progress through the game and get used to the cars, start lowering the assist levels and even turn them off. Currently mine looks like this:
TCS: 0 or 1 depending on the car.
Transmission: Auto, unless I'm familiar with the track and car.
Auto Drive: Usually off.
ABS: Default. Turning this off never cuts my lap times.
ASM: Off on super familiar track/car combos. On everywhere else. This can cause the car to jerk abruptly but WILL prevent some crashes.
Countersteer Assist: Strong
Controller sensitivity: varies
You have Goodwood unlocked, else you wouldn't see the Clubman Cup race. Go to the screen that shows you the available races for any track and select "Circuit Experience". This opens an event very similar to license testing. Turn your assists on and go for bronze on all sectors and the 1 Lap Attack. Winning bronze nets you a decent sum of money with which you can upgrade the Cooper to win the Clubman Cup. Try for Gold if you want but be aware it's fairly difficult.
Goodwood isn't the easiest CE even for bronze, but it's doable.
Once you're able to win the Clubman Cup, you can replay it for credits to upgrade other cars as needed. Later on there will be several more races you can earn more money from, but early game, the Mini Clubman Cup and a few bronze CE's will buy what you need.
On car buying, get the invite cars ASAP, getting invited end game is a pain.