There seem to be five casters in Banhammer's little caster circle (frame 3)
No one in particular wrote:What other casters have been mentioned? There was Marie the predictamancer, Jack the foolamancer, and Wanda the croakamancer... and well, we've met all of them.
, and only Wanda and Jack are recognizable. We know they also had Marie. Now some of those could have been warlords, but based on Jillian's description of Banhammer's low regard for warlords and soldiers, it seems doubtful any warlords would be in Banhammer's inner circle. So that seems like six casters at a minimum.
Stanley also mentions that Faq had a whole lot of casters
. Keep in mind that Stanley at one point had five casters (Maggie, Misty, Jack, Wanda, and Sizemore). I imagine he would think "a whole lot" is more than that, particularly since Jetstone has four (Cubbins, Ace, Pierce, Lloyd), and nobody has mentioned that Jetstone has a "lot of casters".
What's more remarkable is that Faq apparently popped all these casters itself. Stanly had five, but Wanda and Jack were obtained through conquest. According to the Wiki, casters cannot be popped intentionally. Sometimes you get one when you try to pop a warlord. I can't imagine Banhammer wanting to pop a warlord for any reason other than to get a caster. So, unless he had a way to ensure that he got a caster rather than a warlord, Banhammer was popping lots of expensive warlords and then doing nothing with them.
I suspect he did have a way to ensure he popped a caster, or at least to turn the odds to his favor. Maybe he had an appropriate caster -- I would posit a Date-a-Mancer or a Signamancer. Or he had an artifact or even an Arkentool.