Well, 225 is indeed unique in its freighting capabilities... But it was made for unique tasks in mind.
124 makes more sense as a general-use freighter, a rival to C-5.
And on behalf of the flight models - I think that there are not that many parameters that are vital for one. Generally, it is air pressure and, possibly, a wind speed (which could be rather easily simulated, because it is just a vector component after all).
The main complications come with aircraft and engine behavior on different flight modes, but even implementing flight curves and balance curves could bring in some point of realism already (I have little idea though on how it is done code-wise, unless it is matlab's code). Basically all the aerodynamic data is stored in curves Cy(alpha), Cy(Cx), P(H) and balance curves... But again, you have to have the datum on specific aircraft. Failure models and damage models are rather easy to implement though.
edit: I wonder how miserable did I sound with the idea I brought up above as I am studying in aviation university and going to work on Antonov in next year. Do I have to feel ashamed for my knowledge or no? XD