In your opinion

Alright I have a somewhat choice here. My gsx is still stock for the most part. Do you think that i should get my: Walbro 255 lph fuel pump,autometer a/f gauge and oil pressure gauge, wait till after christmas and hope i have enough for my exhaust. I found an n-1 for 450 plus shipping I think that i can get the gt n-1 down piping for a little more as a deal or wait untill my money for school come in and what i dont use get the t3t4 turbo kit? but that won't be until mid january or later.

Get the exhaust. Wait until you have enough money and more for misc parts to buy the expensive turbo and supporting mods. There's nothing worse than having thousands of dollars in parts you can't install or run to it's potential.

would i have to get a new o2 housing or will the down pipe bult up to the stock one

The downpipe will bolt up to the stock O2 housing, or to a tubular housing that you use with a full garret turbo. If you wanted to get it now, there is no reason not to. It will work with your current setup, and with whatever turbo you go with in the future.