4 psi on a small turbo is not the same as 4 psi on a larger turbo
deciding if its safe to tune for a certain psi is worthless information without knowing the exact model and trim of the turbo being used

psi does not blow up engines, power does

for tuning i agree that you should research local options and decide who you trust and want to take it to, i know there are a few very reliable shops in the portland area, then tune with the software they are most familiar with

there are some fantastic turbo build threads to read through, search and read as much as you can, and dont believe everything you read, there are some very knowledgeable people around, and there are alot more misinformed people without very much actual experience

good luck with your project and remember that informed questions will get informed answers