I don't know what the "Sti Back box" is, but the rest of that will run fine without any sort of remap. And unless you're getting the Bosal 2 piece-type DP, you shouldn't need a catless center section with a catless DP. The DP should cover both the downpipe and the midpipe.
You WILL get a CEL though, and I would certainly get a UP before doing the job. May as well take out ALL the restriction while you're doing it. Save the 900, get a UP and either a Cobb AP or a TurboXS UTEC, then you can just run the stage 2 map.