You can play the whole MMO thing as a SP game or as a coop game or you can go online and play it as an MMO but the sp and mmo are separate (the stuff you get in either wont transfer between them.)

You can also play the sq42 military campaign in SP, MP Coop or as a connected MMO experience.

From what they have been talking about though you cant go from sq42 to mmo then back to sq42. You enlist for a Tour of Duty and if you leave during your Tour of Duty you are AWOL. After your ToD you can reenlist or go into the MMO and at any point you can reenlist again.

So it might be best to have a MMO character and a Military character.

They are going to start with the hangar module that you can walk around and climb into your pledge ships. Then they are going to do a dogfighter module where you can just fly the ships and fight but there is no mission or open sandbox world. Then they are going to do the semi-linear sq42 release and then finally after that the MMO release.

Each phase builds on the previous phase and by the time the MMO is out you will probably be tired of the sq42 missions.