reminds me of when i first thought of boosting my car.
Seems like you have most of the stuff figured out. I just want to remind you though, you get what you pay for, and i would like to highly discourage you from buying junk, because it will only complicate things.
I know you can save money going with that stuff, but trust me, it's junk.
As far as your downpipe, don;t drive the car without one. Figure out how to get it to a shop, someone who does mobile welding, or someone who can help you do the whole install.