As I approach the purchase of the exhaust components for my Nomad build, I'm faced with a choice of materials to do this in (mild steel, aluminized steel or stainless steel).
And I'm faced with a limitation of only owning a MIG welder.
And I want to fabricate it myself, using mandrel bent pieces that I can get online.

So the main question here is "can I spot weld stainless components together with my MIG welder, then remove the system from under the Nomad and take the pieces to someone for complete Tig welding?
Does it screw anything up to fabricate it all under the car first, by carefully spot Mig welding each piece as needed to be satisfied with the whole system layout, and then dissasemble/remove it all and take it to a buddy for Tig welding "on his bench"?

Some aspects of this exhaust build I've got sorted out, like going with a quieter muffler like Flowmaster 50 or Magnaflow 3xl. Both are 3 chamber style mufflers, much quieter in interior drone than the equivalent 2 chamber mufflers that have been so popular over the years with builders. Both seem to be made in either stainless or mild steel. And I'm OK with sacrificing a little HP with these quieter mufflers for more enjoyable cruising.

Deciding between going with 2.5 inch or 3 inch diameter system also. I'm only running a bone stock 340 horse LS1 engine/T56 trans, and don't plan to ever have more than 500 horsepower in this thing.

Let's start here. Give your opinion on exhaust materials and the welding question above.