If your going to do it, do it all at once. The biggest expense and time will be the shortblock swap. I definately recommend going with an STi shortblock. They can handle alot of power on stock internals. If you want over 450-500whp, upgrade your pistons or buy a Crawford short block. They have many to choose from. Since your motor and exhaust are out, swap the turbo as well along with the necessay items (injectors, intercooler, fuel pump, etc). Then have a base fuel map flashed from ECUTek, or your EM of choice. You can have it road tuned immediately in order to have the AFR's in line and idling smooth without getting into heavy boost. Good luck and keep us posted.