2k is nasty but we use it without all the flash mask malarkey. Masks should be ok if you're reasonably well ventilated.
Don't use 1k if you can help it.
I've seen 1k smart repairs which we've had to go over with 2k and the reactions they cause in the paint is horrendous. We've had to bar coat seal the previous repair it's causes such a nightmare.
If you spray well enough with 2k on an alloy you should be ok without flatting and polishing. On bodywork it'd be necessary but you'd have to be pretty eagle eyed for an alloy.