I big thing here for me is that the OP already has a lot of relevant experience so, apart from the odd tip, there's not much that anybody is going to be able to offer. The RRA record is well under two days so four must be doable, but the self-reliant rider is in a different situation to well-organised record attempts.
So much of this is self-knowledge: how far can you definitely ride in a day and for day after day and how much rest do you need in between? With that knowledge, it's just arithmetic (and a heck of a lot of hard riding hoping for good luck and good weather once you have done the sums.)
The comment above about flexible accommodation - apart from needing an understanding host - is a reminder that you don't want to be stuck with an unreachable bed, but in the unlikely event that you have a gale force tailwind, it might be useful to be able to ride further than planned on a particular day. That had me thinking about some sort of motorised caravan, but if I knew that I could climb off at any time and into bed, the little voice in my lug would be urging me to do that a couple of hundred yards after setting off.
I think the comments about group riding are very wise. In theory, a quartet or better still half-a-dozen experienced riders of similar capabilities should reel off the miles in a way a solo rider could not, but in practice, assembling the group would be harder than the ride itself. That had me thinking - day dreaming - about paced riding. Once upon a time Bordeaux - Paris was an event on the pro-calendar and on Tom Simpson's
palmarès. Riders rode as individuals and for much of the way they were each paced by a Derny - a sort of moped although not quite the same as the version used these days for the kierin. The principle was that the pedalling kept the pacer riding like a cyclist, but the motor enabled them to go fast enough over 350 miles to pace a top rider. As I said - day dreaming.
