turbo stuff in consideration

well i need to make a pipe to lead to the exaus,air filter, and throttle body...is an intercooler necisary? or do i have to make another damned thing for it?i took a look at my exaust pipes...they join up 1 inch b4 the o2 sensor....do i make a connection from the turnbo there there or move it up to jus one pipe? or split a pipe from the turbo so it reaches both exaust before they join? and do i need a new exasuast system? i have these things in consideration befor anything....do i have to move the O2 sensors?or replace them? and what would i do if a check engine light occurs...any ppiston or rod swaps? replace headers? what if the bolts to the headers break?..and whats the max PSI i should put out...im guessin no more that 6-7 PSI at 5-7000 RPMs...i really want to do this without f***in anything up....

what i got is i have a 6g74 engine...and what some1 said on pajerouk.co.uk forum said is i can swap my pistons wit a 3000gt piston run low boost and have no problem...is this true? or can i keep my stock pistons or should i drop the idea of a turboed monty and get an eclipse/3kgt,evo or a monty that already has a turbo?(im still keepin the current one)