Welcome to the forum!
Mordheim actually "scales up" pretty easily - I have run a scenario with c. 70 models on one side vs. about 100 on the other. It took about five hours to play out, so not quick - but everyone had a good time. I like Warhammer, but don't play that often - we play Mordheim much more frequently. The campaign element is a large part of it, of course. It is fun to see your warband develop over time.