To answer your question 46, I would think any flux residue should be removed prior to bondo or painting. I think you will be better off with the shield gas, as others have alluded to. I tried to save on the cost of a gas bottle and initially used flux core wire in my MIG but it splattered like crazy (regardless of the polarity) and made crappy welds. I make much better welds with a CO2/argon mix.
