Henry, TMG stands for The Master Genealogist which is also an event type of genealogy program like UFT. To find out more go to http://www.WhollyGenes.com/http://www.WhollyGenes.com/ you will read there about the half-price offer to UFT users.
To upgrade from RootsIII may be done by both UFT and TMG. I have not converted from R3 to TMG but knowing the amount of editing after the conversion to UFT then maybe more to TMG I would try the TMG route first.
You should know that the database from RootsIV is the same as used in UFT. If you used RootsIV to read the data after it had been entered by UFT you may find some items unreadable but would still be there.
A lot of work has gone into TMG 4.0a to import the data from UFT.
UFT and TMG would only need the data files. That means the project, library and image folders.