Power Resistance: No
Electricity: Manifesting a sheet of this energy type provides a +2 bonus to the save DC and a +2 bonus on manifester level checks for the purpose of overcoming power resistance.
LoL...anyway,
A73: I would say that, in your first example of them charging through, they take damage in each increment, for the purposes of energy resistances and whatnot, ie (1d6)+x, then (2d6)+x, and then 2d6+x again. Does that make sense? The reverse would happen if you manifested it on top of a creature, and it ran through the energy waves. As far as how often they would take it..... I dunno. Seems reasonable to say that if they're still in the area, then at the start of their turn they take dmg.
P.S. I always like throwing up the ring of energy, focused inwards, and then throwing down Evard's Black Tentacles inside the ring. Good times.