Hi Raptorva,
No offense, but can I assume you have no formal qualifications in aircraft design?
Just a few of your comments seem to indicate a certain lack of knowledge wrt some fundementals.
For example, why do you suppose that, under any circumstances, three engines would be more efficient than two, assuming that two engines of sufficient thrust were available (which, in the size you are talking, is absolutley the case)?
You seem to have some vauge notion that having an "Extra" engine used only when needed (and, btw, aircraft power requirement is pretty much totally defined by power required to takeoff from an appropriate runway at MTOW) would be more efficient than using two, bigger engines.
Not so.
MUCH more efficient in every respect to have two, larger engines, and simply throttle them back to the required thrust.- the saving in weight and drag from the centre engine (ALWAYS an engineering nightmare), cost saving in maitenance and aquisition costs- the list goes on.
The only reasons we ever had tri-jets were because sufficiently powerful engines were not available, and twins were ham-strung pre ETOPS.
Sorry to pour cold water on your project- stick to the twin, and you look like you have something very like the new Mitsubishi RJ.