The event horizon is a null surface, and as such has a coordinate area, not volume. I'm not sure of the relationship between this area and its angular momentum, all else being equal.
Yes, a rotating black hole (Kerr metric) contains a ring singularity.
A charged black hole (Reissner-Nordsrom metric) cannot have its charge exceed its mass. So no additional charge can be added to one that is sufficiently close. The mass in unaffected by this, and the event horizon 'radius' is determined by the mass.
If there is a black hole with charge equal to its mass, you get a naked singularity, which is a singular solution to the metric. So (just thinking out loud here, not an authority), if you have a super-positive charged black hole near this limit, a negatively charged particle would be more attracted to it than a neutral particle. Thus I would think there would be a second charged event horizon for the negatively charged thing that is further out than that of say a neutrino. Also, the EM potential would be so steep that it would probably rip apart (an EM 'tidal' effect) neutral things like a neutron, pulling it into charged components and accepting only the one.