Using De Bruyne as a center mid is the same as using Silva as a center mid, technically it can probably work but it's kind of a waste, in fact Silva might even be better than De Bruyne there because while neither of them are great defensively Silva isn't afraid of going in for tackles and such, plus he's also a better dribbler. De Bruyne's one weakness is that he's poor defensively, and it's one of the reasons Mourinho let him go from Chelsea.
Either way I think 4-2-3-1 will be best if we get De Bruyne, 4-3-3 should only be used against attacking-heavy teams like Arsenal or Barcelona where we need to be more responsible, in which case we'll probably have to bench one of Sterling, De Bruyne or Silva. I think once Silva ages and he'll decline/need more rest that's when we'll switch to using 4-3-3 primarily.