I definitely recommend changing transmission fluid as more of priority. it's my understanding that from the factory it's not always filled correctly and may be a reliability issue for the transmission.
intercooler just wait around and you can probably snag something like a whoosh v3, cp-e, moutune for a decent amount.
I'd also check out the $15 bolt for the passenger engine mount that may be an issue. seems like a pretty cheap fix.
https://whoosh-motorsports.myshopif...r-engine-mount-bolt-upgrade-kit-free-shipping
totally agreed with radiator.
I always recommend getting an alignment with any car you acquire. my latest new car, my '18 camaro was night and day difference after getting a 4 wheel alignment. for better or worse with the fiesta its usually just the front wheels. after getting camber bolts, should be more or less $100
I think radiator, intercooler, transmission fluid levels aside this car is pretty well optimized from the factory. usually 100% I would say jump on things like better tires, sometimes brake pads, better brake fluid, do some suspension parts for other cars, but for for the the fiesta everything is well optimized for fun street driving. the stock suspension, tires, pads are really good. unless you're a fantastic driver, I think much of the upgrades you will see only if you hit the track. Hoping to hit up Chuckwalla this weekend and I'm very comfortable doing so with more or less stock suspension.