Yes, Leadership is still a good skill line to take
As for nature affinity, it depends on your goals, I like high-recharge builds for it, so I've got the following powers slotted as such:
Regrowth - 6 Preventative Medicine
Wild Growth - 4 Recharge/Resistance IOs, 1 end redux (thats really only necessary on an MM)
Spore Cloud - 4 Dark Watcher's Despair
Wild Bastion - 5 Panacea, 1 recharge
Overgrowth - 5 Adjusted Targeting
Corrosive Enzyme is a 1 slot wonder power, just an accuracy will do.
As for Epic pools, Mace mastery is always nice because it provides defense.
Soul Mastery is great for power boosting Regrowth
Rune of Protection in Sorcery is a great power, as it can act as a break free. Not an epic pool, but just a thought.