Erfworld Pbp campaign [d10, GURPS?] - mechanics advice requested

Hey guys, I'm planning on running an Erfworld campaign with the players barbarian warlords being hired by the local sides, like Jillian. The setting would be lowish magic, with only magic items. Most mechanics will be taken from the comic

There will be a few mass battles.

I was thinking of using the d10 storytelling system (WotD one) with stack bonuses and leadership bonuses adding on +1 die per point of bonus, and specials such as Riding being bought with character points.

My main trouble is how to create the enemies to be challenging, not too weak or overpowered. However other people have suggested the GURPs system, what do you think?

This is my first time playing or running the d10 system