electronic boost controllers tend to have an upper limit that they can handle (usually indicate the rating). I don't know how they deal with the wastegate once they get there, I guess it depends on who programmed the controller. i would think it should punk out and open the wastegate.

Manual controllers can essentially hold it shut forever.

Either way you should be able to make way more boost then the hard parts can handle.

Boost then is limited by the turbo's match to your setup. Big turbos take longer to spool. If you go too big, you may not be able to spool a turbo to where you want it. Opposite with small ones (except too small, and you get out of the turbo's efficiency and you effectively are super heating the air)

Ideally you get a spring rated the closest to the target boost level you want to run. It usually helps with fluctuation.

Also know, that an indicated spring # number doesn't necessarily tell you how much boost it will equate to. On my truck a 15# spring from Innovative (race gate) nets me about 7-8 psi base. This depends on a lot of things however. I think the biggest in my case is exhaust pressure. The numbers may be closer on other applications.