He'll need different software before you start adjusting it or it will just boost cut on you.

There should be a vacuum pipe already in the throttle body that you can T into that will operate the dump valve

Its a KKK turbo

TBH i dont know a massive about about the Z20LET series of engine, its a bit modern for me, im more a C20LET guy, so posting on migweb is a good idea as i dont know the exact details of what chips are best etc.

cossie 4wd cooler is fine in terms of cooling performance, but you will need to make sure you can fit it somewhere physically, which i havent ever tried on that car obviously as ive not had one.