There were only two "body styles", the hardtop and fastback.
There were only four "models", Coupe, Ghia, Mach 1 and 2+2.
Everything else (Cobra II, King Cobra, Rallye, etc.) was a package available for one or more of the models.
The Ghia is set apart from the coupe by luxury appointments and the Ghia symbols. Some coupes were available with the vinyl top so that in itself does not set it aside from the Ghia.
About the Ghias, the Haynes book says: "Top of the range is the Ghia, which must be one of the most luxuriously appointed small cars. Extensive use of sound-deadening material has been made and suspension-to-chassis insulation ensures a level of quieteness comparable with much larger cars..."
The Fox bodied Mustang starting in '79 had a Ghia model in '79, probably '80, and maybe '81. It was a pretty good looking car with the same sort of luxury appointments that came on the Mustang II Ghia.
The later GLX was considered an upscale version, but the LX's could be ordered really stripped. I don't remember either as getting the special attention from Ford that the Ghia got.
The term "Ghia" comes from the Ghia styling studio in Italy, bought by ford in the late '60's -early '70's as a way to give some European flavor to their line and to get rapid prototype work done. Before its purchase by Ford, the Ghia company did styling work for several manufacturers, hence the VW Karmann-Ghia and earlier Chrysler Ghias.