Ability to keep mandarin is a function of a sustainable pod population. This means refugium, maybe RDSB, and a lot of live rock. If you can manage this on a FOWLR then yes; if not, no.
Yes. Kept with it dwarfs angels, smaller butterfly's, wrasse, Hawkfish, and tangs and mine did fine. It died when I added another dragonet and they fought and my first one died.