As I’ve found with my own car, there’s really no limit or boundaries... and for the most part these cars aren’t really all that special, yea to us they are but not every Porsche is a unicorn and should most definitely be modded or hot rodded to reflect the owners personality.
I would recommend however that before endeavoring to change anything you spend some time contemplating exactly what you want both from appearance and drivability and then set out a master plan. It’s much easier to renovate a house with plans than to dive head first and wing it- without a guiding vision it gets very expensive and there are constant changes and lots of time is wasted.
With a master plan you can budget your money and time such that you don’t miss out on driving it yet still have the project moving along.
As for the bumpers- I was in the same shoes and started by lightening them up, then I started to tuck them and modify them a bit and then after all that work and time spent (and luckily not much money) I decided to go with fiberglass bumpers. I wish I would have thought about it more in the beginning as I would have saved a lot of time and swearing
Anyhow, good luck and keep us posted!!!