Seems like you are pretty well there on the sheet metal now but for future reference.
I take the factory seam sealer off several ways. Dry ice works great, make a slurry using rubbing alcohol. Hard to put this in wheel wells though. For that, I burn the s*** out of it with a mapp torch. Then hit it with a wire wheel on the 4” grinder or on the die grinder. It is dirty and nasty but works good and doesn’t waste expensive flap discs.
Also, if you are worried about zinc or can’t get it clean enough for good welds, the SpeedyBlaster is the tool of choice for prep. I got a blast cabinet too and sand blast as much as I can for welding prep these days. I buy a new bracket or make one, it gets blasted before any welding.
$500 CL score plus a few hundred to fix it up.
Cheap, messy but works good for anything on body/chassis.
As you figured out, .23 for sheet metal. I turn up the speed a lot too. Allows me to lay beads vs tack tack tack. I of course start with racks and control heat so no warpage but 2”-3+” beads is no issue.