be prepared for the fact that riding for that long (simply time, rather then distance) puts a lot a strain on bits of your body that aren't used to it – shoulders, wrists, neck. also it's a fair observation that 15mph for 17 hours seems *very* fast average, when you include stops. there will be stops!
also riding for that long on main roads, especially dual carriageway, whilst shortest and quickest, will be very tiring due to the traffic noise/wind blast from vehicles at 70. lots of riding without being able to talk to each other.
don't want to sound too negative, sounds like a epic plan, but best to go in with full knowledge than get demoralised early on as the unpleasant surprises hit home!
the escape plan option is a two edged sword! it can make to feel like you can push yourself really hard knowing you can get yourself out of trouble, or it can make you give up far before you need to simply because you can….
keep eating, even if you don't really want to , lots of calories to get through. mix savoury stuff in too – hours of eating sugary food can leave you unable to eat *anything*!
defo start as early as you can, 0300 or 0400, and make sure you're well over halfway before your 'halfway' stop. makes a massive morale difference.
enjoy!!