Weld with your back side to the wind so any fumes are blown away from you .. If needs be cover two sets of gate with canvas or sacking to get an air funnel going behind you or angle two vehicles behind you for the same effect .If you've got a blowtorch you can burn the galv off but it can be a messy way to do it...
and you still wanna grind the 4mm edge...
You need an assortment of angry grinder attachments - flap discs, 1mm cut discs as well as wire wheels...
Various manual wire brushes are handy too.
Seems like Tool Shopping is required !
Whichever method you use, wear a mask so you don't breathe it all in...



