To be able to handle running all of this, I've instituted a policy of running pre-written senarios. There's a lot of really good pre-written senarios out there, and I own quite a few myself. So now I find myself hunting through my books looking for a good adventure that would work for the 1920's and this group, which is based in Boston. It takes a while - I've got a lot of books and some of the adventures don't exactly fit what I have yet, or they're for groups a little more experienced than mine. (And since my wife is playing, I have to be sure to skip over adventures from my previous campaign, which she took part in.)
Tricky. But fun. One of my favorite bits about CoC is how much running the game feels like being in it- searching various musty old rpg manuals looking for the bit of eldrich lore that I need.