16g has a mitsu turbine housing so you dont need a new exhaust manifold. you will need a j-pipe though for the intercooler piping. and depending on what it comes with you might need some other things like oil lines, maybe the o2 housing, but nothing big.

if you get a t3/t4 you have to buy a new exhaust manifold and probably a wastegate along with o2 housing stuff and oil lines, some new intercooler piping and stuff like that.

in short, start with the 16g, the big turbo is gonna be useless if you arent setup for it.