I've been a sheet metal worker for 20yrs, & the best thing is a 5" Makita grinder with an electric brake. You have to modify the guard & make your own to run a 6" skinny wheel. OSHA says 50% coverage, I like about 40%. It keeps the sparks and grid debris from rolling back on you, & helps deflect the sparks. I'm currently not running a guard, only because I haven't taken the time to build one for the grinder I'm using. But the are a good idea.
Most of all, you need to use wheels with a metal arbor, or I've seen these things take off like saucers. Anyway you look at it, they can be dangerous. You can't push them too much, & you can't get them in a bind. Especially, if they get a chunk out of it. Just got to be careful... You can take your eyes out kid!
Gloves are a no brainer!