My $0.02....
1) Unless you have an E4OD or plan to do a trans rebuild I submit that the Haynes manual is sufficient. The engine info is directly from the Ford book and sufficient for an engine rebuild. Most of the other mechanical stuff is pretty generic. Really don't need too specific of info to change an alternator...... The OEM set does have some nice top have info, and would be important for electronics stuff (though the Haynes wiring diagrams are much easier to use than the OEM ones I have) and some of the body stuff. I would say it's a nice to have, not a must have. The point is that the Haynes is a good start/cheap and easy reference for someone that doesn't have the money or time/luck to find a factory set.
2) The list of manuals is likely somewhat year dependent. For the mid 80s (84&85 that I specifically have books for) there's the following in the complete set:
'A' E/F 150-350 Body/Chassis/Electrical
'B' E/F 150-350 Engine
'C' All truck Pre Delivery
'D' F,B & C 600-8000 Body/Chassis/Electrical
'E' F,B & C 600-8000 Engine
'F' Ranger/Bronco II Body/Chassis/Electrical/Engine/Pre Delivery
'HT' All car/truck Engine Emissions/Diagnosis
There is also a separate specification book, wiring diagrams and the EVTM book, although I've only ever seen it for E-series for some reason.
With the books I have, the 'A' & 'B' books are the most useful. EVTM is nice as is the spec book. The 'HT' book is pretty much useless for the diesel. Would be good for a gasser though.