VF39 is a nice little turbo until the WG cracks.
I've herd allot of complaints about the SZ55. I would personally stick to a 20g. But some people seem to like the SZ55.
I've got a SB gt14 waiting for me.
As for idling the car. I still idle my car a little bit if I've been beating on it. My car drinks nothing but full sync. I only use BP93 or Sunoco 94. Make sure when you research you car to find out if it need a Intake and other shit. The WRX / STi don't need upgraded intakes till after 300whp. I'm stock intake down to the paper filter.
Avoid MBC's without a tune. It just a bad idea the car can compensate to a extent but over all a good tune > mbc. Or a good tune with a MBC.