That is not for me to say. I only wanted to put the warning out there, as a society game and play-by-email RP veteran.
Note that such PvGM+PvP games can be loads of fun, if the OOC / IC wall is kept up at all times. However, some players are either unwilling or unable to do so, through no fault of their own. Why give them reason to extend an in-game vendetta (which can be very fun to pursue indeed) to a RL grudge (which, usually, is not)?
EDIT: Spoon, just making sure that you've noticed, but I've added a concern in y earlier post (see three posts up, bright yellow). Could you address that when you have the time, please?
EDIT 2: Also, I expect you have a decent counterweight for planning to give the DD only 2 pieces on the board - first impressions of the game mechanics seem to show that fleets are the most important variables around. More fleets = more options to earn PI, new real estate, resources etc. It definitely looks like the DD can't even trade to gain power: their PI is abysmal in regards to the other factions and they'd come out the losers in every deal.
Now, of course, since I'm a DD player, me noticing perceived 'imbalances' regarding my faction first is expected (and evil and impolite and a nuisance to the other players and yourself, Spoon). Please do not consider the above a complaint, just an expression of curiosity regarding your planned approach to balancing out the factions.