Seamus can be really dangerous. In one of the games I played recently he got to a graveyard and could pop out a new belle every turn. If you take the Resurectionist scheme it's almost a sure thing.
The belles work best in large groups use one to lower the stats, one to lure then beat on them with the rest.
I'm still trying to make sure I have all the rules down, but each box seems to have some synergy. It seems that at 30 SS you'll get the most out of the game, adding a few models will shore up any glaring weaknesses.