Oof, maggots aren't good at all.
As I mentioned in my last post here, trimming would be a good idea. Giving a "butt bath" when needed would also be good.
Pasty butt refers to chicks that have a block up of poop stuck to their bottom, that keeps building up if not taken care of. For older chickens it's not called pasty butt, it doesn't really have a name, and it's not so much of a problem as it is for chicks.
How's your weather? If its hot they'll...