Yeah, that sounds about right.

I think it just depends on what direction we want to take it. If we're going for an almost apocalyptic feel, then more than 60% for sure. The thing I see is that The Empire has been at large for more than 10 years, slowly building their forces until they were able to strike -- Disney Castle being the first world to go under their control. Actually, I see Disney Castle being The Empire's base of operations. 

 As for how the Empire works, this is the way I see it.

The non-heartless/foot soldiers would work in a similar way that the Archadian Soldiers do in Final Fantasy XII. They're armored up and pose no real threat aside from the number game. 

As for how the heartless would be deployed, I think you nailed it right on the head. They are simply following their new masters. As they did with Maleficent in Kingdom Hearts 1 and The Organization XIII in Kingdom Hearts 2. If you want, though, we could try to put some original spin on it. Though, nothing really comes to mind at the moment.