-No Flash Hider (only muzzle brakes and compensator)
-10 round mags or smaller
-No incendiary bullets. Dunno if hollow points are legal, but staying with FMJs will be savvy.
As far as the state is concerned, if you have a bullet button installed, a flash-hider or brake is a non-issue and there are no restrictions whatever on ammo that are specific to an AR platform. If the ammo is legal to shoot in any other rifle, then it is legal in the AR. The incendiary/trace bullet restriction applies to all ammunition in the state. Hollow points are perfectly OK in an AR ... there are not even any gray areas about it at the state level. Maybe there are some local restrictions ... I don't know.
Again, as far as the state is concerned, there are no restrictions on "features" for an AR built with a bullet button (grenade launchers are prohibited by a completely different set of statutes, but those are not available for the AR anyway). CA has a more restrictive minimum length than BATFE, but I don't think that I've ever seen the parts that could make an AR go below that length without being an SBR by BATFE rules anyway.