Q1. Did you build the support structure that is attached to the rotisserie? And do you have the details and dimensions? Yes I built all of it, including the rotisserie. The car sits on 2x2" 1/8 wall tubing, should have gone 2x3", that is why there are braces added. Where are you? I hope to be done with it soon.
Q2-5. What were the specifics on the plug welds? Size of hole you started with? Do you grind the weld spot flush afterwards? Type of welder/settings/wire, etc? I experimented with different hole sizes on scrap steel. 3/16-1/4" hole works well, smaller for thinner, larger for thicker. Hobart 140 (120V) MIG on high with .024 (.6mm) wire, C25 gas, clean down to bare metal, cut wire off for short stick out, position gun 4mm spacing, then trigger for 2-3 seconds . I grind them afterwards, but if you are good the hole fills and is flush
Q6. I see the bracing on the inside is bolted thru an existing hole but I can’t tell how you attached it at the front bulkhead? Used old bed rail that I pick out of trash, that included 90 degree end piece bolted to door mounting points, you are welcome to the bracing as I am done with it.