Impossible Mode: Paladin Skills and Order

[Alash]

I've got a level 21 Mage on Hard mode, and although he's doing well with his back-to-back 8k Geysers I'm just not sure it will scale as well on Impossible mode. And being a competitive person I really want to complete this on Impossible. The Paladin seems like he mixes the power level of leadership with the mass effects of the spell tree, so I've decided he will be my choice for this project.

Question is now, which skills to take, and when?