You could make that into a very tasty loop if you rode:
Day 1: Spean Bridge to Meanachan bothy (maybe the other way round from your guide book, but this offers better riding I think).
Day 2: Down from Meanachan to Kinlochleven via one of several great descents, breakfast at the Tailrace, up and over the staircase to Glen Coe, then back up and over, finishing with the Ciaran path and a night in the hostel.
Day 3: West Highland Way to Fort William.
Day 4: Red Route, train home.
I'd definitely run tubeless, with burly tyres. Lots of rocks and jagged waterbars. The best weather would be may or perhaps september. May is early midge season, september is the beginning of the end. I'd be more worried about the Kinlochleven clegs, they bite through clothing!
I'd just carry a sleeping bag and a mat. Worst case scenario is that the bothy was full and you had to descend all the way to Kinlochleven to stay the night.