All that white stuff on the panel is zinc which has been burned by the welding. It's good that you are welding outside and there's not much of it but still take care not to breathe it if you can because some people are more susceptible than others so you never know how it will affect you. You'll know if you get affected because you'll suffer flu-like symptoms. It's called metal fume fever.
TBH grinding that zinc coating can be as much of a hazard as welding it. I'd find some clean material.
If there's any sheet metal work/fabrication companies nearby you might ask them for scraps from the guillotine. Explain that you need it for welding practice and even say that you'll bring it back when you've welded on it and throw it back in the scrap bin, that way they still get the value from the scrap man.
What part of London are you in?
Looks like a Golf MkIV wing, probably nearer 0.75mm than 1.5mm thick. Nice even beads for a first go with gasless wire on thin sheet, you will notice a difference if you go to solid wire and Argon/Co2 mix gas.
The helmet brightness is up to you. If you are fairly young, you can probably tolerate a brighter setting because your eyes will quickly recover from the light. As we get older, the recovery takes much longer so we would be blinded by a setting you would find OK. Even at the brightest setting, there is no arceye risk.
Slightly Off topic. But does anyone else think that the surface of the wing looks a bit like Zimmerit? the stuff they used to put on German ww2 tanks...……………...or is it just me?
my mask is dual range i tried mig on the lower range and ended up with bright spots in my vision for a few mins after welding pretty sure its for low amp tig.
You will certainly get your practice in then! LOLI had to google this, but yes, you are right. Maybe I should do a whole car!