Please be sure security is addressed early in the game. This is similar (yet more complex) to Pocket Empires, which has faded into obscurity because hacking and cheating was everywhere. Once multiplayer launched, people had armies in the billions, which was illegal. It wasn't fun anymore, and people quit.
If you want to make a pay to play game, please make sure it is fair and there can be no cheating. Otherwise, it will be worthless to pay for a subscription to me.
Also, will there be an option to buy the game outright and avoid a subscription charge?