If the 5.2 questline is any indication you'll need to do both PvP and PvE participation to keep going with these at some point. I'm having to do battlegrounds now to finish the 5.2 quests for battleground wins.
I'd guess that since this meta is for all melee that the stacks will work on an RPPM system otherwise classes with fast melee attacks such as rogue would be out of control with the procs and damage. It will probably stack about as often as Raining Blood in Dread Wastes if you ask me.