ive purchased a ported and polished head and a t4 for my cosworth 2wd with 4x4 engine

its currently standard engine with greens stage 3 chip 3 bar group a gasket rs500 intercooler etc

should i go get a stage 4 chip and greys what sorta boost would i be able to run with greys or greens with the t4?

should i get a wrc headgasket or is a grp a enuff?

jus luking for sum advice really