I dont have any landy experience of 'expedition' type trips.. but i do have quite a bit , on a yamaha XJR 1300 motorcycle, and the methodology & thought-processes are very similar i guess ...
I'd advocate paying a fair old bit of attention to what Storm is advising on here ... its going to be a big undertaking, and it'll knock the bejeesus out of you physically, even if you're very fit and financially-speaking, it'd be a 'no brainer' ...
Consider also - look at most modern cars which have an on-board comp' .. check the 'average speed' readout, and invariably it'll be somewhere around 32 - 35mph, for a vehicle that often sees high 80's Dual carriage way cruising, mixed with town work, and back roads tootling, plus commuting. You'll definately struggle to 'average' 50mph.
Sounds like Mr Storm knows his onions here .. and my experiences of 'mega run' biking would bear him out too.
Seriously consider what he's advocating there...
Dont wish to 'preach' .. but I reckon i'd give what he says some serious consideration before getting in too deep