Help me choose intake piping size

Hello everyone,

So i hope i've illustrated it on the picture below, basically I'm not 100% sure which piping diameter I should go for in between turbo > intercooler > throttle body.

I'm not 100% sure what I should do with the Turbo to intercooler inlet, as the difference in size is significant, however, the piping here will go small to big (turbo as being 67mm (external diameter) and intercooler inlet is 76mm, so definitely no backpressure here.

The more concerning thing is the intercooler outlet, 76mm and throttle body , which is 67mm for internal diameter and 73mm external diameter, what I should do here to avoid any backpressure?

Thank you

@Andre.Simon