Yeah, just start with a Subaru engine if thats your end game. Gutting the dash only saves 40 pounds, I have done it 3 times now and weighed all the parts and all 3 times I lost right about 40 pounds. The ac stuff isnt much more, but every little bit helps. I think you will want to keep as much floorpan as you can, thats a part of the cars chassis.
A turbocharged STI engine would be pretty sweet. They make like 305 hp stock, thats 50% MORE than your vw goal. Only doing it once is the best way to go. Im going through that right now, only this is my 3rd time installing a different engine in my car...