Since I am GMing the Mutliplayer game that panop first created I can pass on some good details to you folks.
1) Diplomacy will only work as a GM option I bumped up all the Diplomacy to 100,000 and left it there. This way as a GM I can choose the tension level, research trades etc etc.
2) Anymore then 5 player blocks in the same system hammers cpu, mainly around sensor contacts. If you want to play with high number choose not to all start on the same planet.
3) Time dedicated as a GM you have to be dedicated to put in 5-8 hours per turn, that could be a week, 1/2 week a day. But you need to sustain it which is the hardest thing.
4) I have gone for a highly detail approach, this in itself has cause issue when you make mistake, miss some note etc etc. My suggestion here with thought on this matter for a while is this.
Set up a dropbox with faction folders, allow the players to drop there beginning changes into the box and pass to the next player, remembering to set it back to the default race (reason if you do not have a default race on entry you do not need a password for the last race exited.) Then you say to the players you will only get involved for the sixth month period if there is combat or an emergency. Orders can be set with delays, production and research can be queued.
This would make the GM work very light and and the responsiblity is on the player and you may be able to get turn around quite quick but need dedicated players or a group of players playing a bloc that makes sure player turns are moved quickly to the next bloc. Also the flow of the game is up to the players as the GM six months would not be harder then an 30min to an hour of pumping over turns. Then uploading with no further details.