Trollbloods #1

I'm doing Trollbloods, and am already hitting a roadblock inspiration-wise. I have two areas to decide in:

1) Warlock! I've narrowed it down to Grim Angus, Grissel, and Calandra. Not sure who to pick beyond that.

* Grim I like for his speed. I'm coming from a Khadoran background, so thats a nice change. He's decent at running beasts, which is key to me. He has lots of movement shenanigans in his army too.

* Grissel I like for her Fell Calls and support role in the army. Again, this is something I don't get a lot of in Khador (where I play Butcher armies!).

* Calandra I like for again, her army support, and the fact that she's primarily a spellcaster, something new to me.

I have all three models to choose from, and would appreciate thoughts on the matter.

2) Theme! This is in regards to colors, basing, and army comp. After my frozen north Khador, I want something different. A swampy theme sounds good, but I don't really know how to go about doing that. How do you make a model look like its in a swamp? Failing that, I'm open to ideas. I have a green & white army, a grey & gold army, and definitely don't want to do the PP-standard blue trollkin army.