I also think Epcot should be the first stop. The Flower & Garden Festival will be in full swing with concerts and seminars too. It's more "adult". Make the MK your LAST stop and by all means avoid any Character meals initially.
Next, take in a Resort or two. Maybe the BoardWalk area, since it's close to Epcot. Have your DF check out the restaurants and clubs there. The Animal Kingdom Lodge and Wilderness Lodge are gorgeous stops also. The themes aren't "cutesy" like other Resorts may be perceived to be (by a non-Disney fan).
Does your DF like sports? Include a stop at the Wide World of Sports complex, a golf or tennis day or rent a watercraft (maybe at the WL).
Of course, there's PI for more clubs, etc.
I'd say that your DF will soon discover that WDW is huge and offers something for all ages.