Berserker pures basically need to get barrows gloves (you need to do some quests that give Defence experience for it). Other than that, there are no other requirements than staying at 45 Defence.
However, to get some rewards you may want to do some extra quests: Temple At Sentisten (for Ancient Curses), In Aid of the Myreque (for Burgh De Rott bank, useful for Barrows) and lots of other quests (you'll have to find them yourself).
I haven't seen any complete, detailed and dated guide around, so you'll just have to look around and do as many quests as possible.
Holy Grail / Olaf's is optional. The rewards aren't worth it, IMO. Holy Grail is required for King's Ransom, and surely a berserker pure wouldn't do that quest. And Olaf's Quest's rewards are just pathetic.
You need 70 def for piety. Imo do be a successfull rune pure in rewnskep, u need to be 45 def with barrows gloves, use overpowered weapons the whole time you are pking and if u wanna really own, get turmoil.