[Jtrux]

Yeah one step at a time. I'm about to be in the same boat, I know my B pillars are junk but I think my A pillars are decent so I can't offer you advice there but i've gotten some sheet metal welding experience recently and I can tell you that fitment is everything. I'd be tempted if I was you to start over cuz when you begin to weld it you want as little gap as possible. Even if the original metal you're welding to is in decent shape it's still gonna be tough to weld through and you can expect it to blow through if you have any gap at all. I would try to keep the gap to about the thickness of the welding wire if possible to minimize having any issues with it.

Hope that helps.