Hello and welcome!
It sounds like you already know how to make your car quicker
Once you have remapped the car, the power increases can often have deminishing returns, so for the remap, it has a significant gain for not too much money, then to get a smaller additional improvement, you have to spend quite a bit more - and once you start spending a lot of money, you may have been better off getting an ST in the 1st place
On top of that a bigger turbo and intercooler can add a lot of turbo lag - ithas been said that although the 1-litre ecoboost- engined formula-Ford (with ST turbo) had 200Hp, the power/ throttle was like a "switch" (poor drivability) which may be ok for a very lightweight "race" car, but not so good for a heavier road car
Nevertheless - im interested to find out what will be possible (and still driveable/ practical) myself