I like the idea of a female druid. I still haven't decided what it will look like but I'm leaning towards the 'furs and skins' type rather than another robed unit. A female druid would suit this unit well.
The abbey should definitely be able to store gold like the necro tower!
On the extra resources point, I don't think extra resources are really needed as they will just complicate things. I am interested to know whether resources are hardcoded i,e you can only have 5 different resources, or whether this is just a limitation of the mapper?
On unit names:- White knight and paladin are fine (paladin is somewhat cliched in the fantasy genre but its still probably the most suitable!)
Personally I think monks should stay the same. They provide piety points and they also have a near insta-heal ability. I don't think they need to have an attack since they are monks. Possibly they could have some kind of beneficial buff for nearby units?
The treant idea is great

Treants should be able to camouflage themselves. Basically the treant should have a 'tree form' ability which basically morphs them into a standard Glest tree which can't move or attack. This allows players to set up ambushes and spy on the enemy. Unfortunately two things need to be done to make this work. Firstly there has to be some way that the enemies will not recognize the tree and attack it (also it shouldn't show on the minimap). Secondly the big problem is making the tree match the chosen tileset. Having a palm tree in the middle of an icy waste is gonna give it away!