I agree that the starting cash probably isn't enough of an advantage throughout the game. Maybe there could be another small long term advantage as well (they could receive slightly more gold when selling wyrdstone due or equipment and new warriors could cost slightly less as well *due to their...
The more fish the better - there was a very fishy aesthetic to the original game. A lot of models had a fish somewhere on them (even covering their head in one instance) and the rulebooks were choc full of them too :)
Definitely throw in my vote for Dwarves to make an appearance. Some thought they were overpowered in the table-top version, but they were easily outnumbered and very expensive to start off with. A brilliant gang to play with, full of character, and this game definitely needs a troll slayer :)
In the tabletop game, my mercenary gangs ALWAYS had an ogre! Heavy hitting, fear causing, damage soaking brute! And the original Mordheim Ogre miniature is gorgeous and easily one of my favourites of the whole range!