ok i want to build a set of headers for my bc5 legacy turbo ej20g

mods are

gc8 fmic
TD05h 16g
chiped computer and safc
sti yellows
2.5" wrx exhaust to freeflow muffler
walbro 500 hp fuel pump
aggresive reground cams

i plan on turning boost up to around 1bar or a lil more

my question is for an expert or somebody in the know

what size piping should i use ?

for the primarys?
then the collector?
and the uppipe to turbo?