Find someone local who has the kit and ask to have a play, start on nice thick stuff so you don't just explode it - you have lots more time to see what's happening and get a nice pool of weld going.
That's the easy bit...
Translating that onto thinner materials or joining different thicknesses while under the car with a trolley jack digging in your back is where it becomes more challenging
Seriously, it isn't difficult, just takes time and patience to learn, so someone on hand for advice will make a big difference.
Auto blinky masks are silly cheap - like £30 or so on the 'bay.
Get the best mig you can afford, higher capacity will have lots of headroom so you can weld bodywork all day long without it tipping over in a hot flush - but make sure it still has low enough settings!
Gas/gasless is most flexible, so you can run flux cored for convenience or outdoor use, then switch polarity and use gas for really thin fiddly bits or where you want a cleaner weld straight off. Flux core splatters more, heats the surrounding work more.
I dunno how peepl manage with out the magic glue gun for metal
