In Fact im using my Rev Jr hooked with avatar cabs, go for it , you´ll not regret. speakers go V30 of course, if you want it just for the Rev Jr. maybe Greenbacks will serve you well too.
Yep, but open back is a really nice option, i have both, open and closed, and both sound great and have great low end, but for metal, closed, if you want more versatil sound, go open.
eminence v12's. not what i'd call generic. they sound pretty damn good, actually. if you want to upgrade, my advice is to stick with a closed-back cab and use either V30's or EVM12L's.