Personally, I'd start by looking at the TMP Excelsior design, then the TMP Constitution refit, then the TOS Connie and then look at what sorts of pieces could have been upgraded from TOS to the TMP Excel.
I'd think nacelles, secondary hull, deflector, bridge module, impulse engines, nacelle pylons, lower sensor package on the saucer. Secondary hull should roughly the same size seen from the top view (that appears to be a design feature).
Personal opinion, I wouldn't go for as much bling as the shiny disco ball version, I'd go more the Helena route. The disco version is very pretty and all, but I kind of see it as Olivia Newton-John in Xanadu.. she was gorgeous then, but how well did she weather?
My two cents..