Declare?
I'd rather ask, most of the time, or make sure everyone knows how the various groups are going to meet up and keep everything from dissolving into a continuity mess.
Splitting up parties this size=good. I don't want every battle I have the PCs fight be stupidly high level just so it can survive a turn or two against a dozen glass cannons. It's ridiculous. I don't want to have to split them up in contrived ways, either, and sometimes I don't even know what PCs are in the area because people will just pull their extra characters out of nowhere, it seems like.
Then again my characters are perpetually in nowhere, so who am I to talk.
Anyway, I just keep coming back to the megacorp campaign, so...think I'll probably end up going with that, though it'll probably be something that will end up being either a massive clusterfuck due to the stringent requirements on my time (not supposed to use Internet in the morning, or at school, or at swimming(duh) and then I have homework and chores that I also have to get done, and past 7 I'm not allowed on my desktop, and while my new laptop is very very nice, it'll a far larger pain in the ass to run turns on, I can already tell; all told I get around 3 hours of comp time to spend on any and all of my games and/or browsing the internet on most weekdays, which is why I'd be piss-poor at running turns, especially when combined with my nasty habit to procrastinate), or it'll die. Even though the size and scope of it is the type of thing I want to rope a quarter of you into assisting me with lore and would drastically change the geopolitical landscape of the world because Status Quo is the enemy of Plot Development, and nothing says 'urgent' like trying to decide whether to help Murder Night stave off a Void Sultan or letting her handle it so you can stop the Greater Balrog of Fiery Deathpenis from taking over large portions of Siberia.
Also working on the turns.