Several years ago, when I lived in Bologna, I used to organize many Campaigns (from 4 to 8 participants).
I managed these Campaigs with basic methods and devices (written orders on paper, sporadic use of e-mail) but it was more than 10 years ago...
Moving some pics from my smartphone to Dropbox, I found the pic below.
It is the only pic I have from the last Campaign I organised here in Terni (when I had a group to play with): it shows the master map I used (yes, it is 1812 in Russia :-). As far as I remember, 6 players took part in this game. I conceived a nice and easy system for orders transmission, a system that allowed me to participate and not only Master the campaign. Once a week we met on Skype (chat) and we declared our orders, starting with myself. Three turns (approx. 6 days of campaign time) had to be planned and declared, so that the fog of war was still quite high (it was impossible to change the orders once written and shared on Skype).
When 2 Forces met in a point, a battle ensued.
We used a simplified combat system (DBN like) and fought the battle during the week, so that on the next monday we were ready for a new strategic phase (orders).
This was - and still is - the only Campaign played by my - former - group and the only long term activity that was finished (with a Russian Victory btw.....).