Gonna be honest.. not a big fan of the seat. Not only do I think the shape/size doesnt work with the tank at all, but I cant imagine that mounting that thing will be anything less than a nightmare. Also while I do like the shape of the tank, I think the way that it slants up as it goes back is going to make having a seat flow with the same line very hard because of the shape of the frame.
Hope I havent rained on your parade too much. As I myself have done a bit of fabrication in an ill-equipped garage workshop, I know its not easy, and you definitely get respect for diving right in.