If you still have some time before the ride, I would recommend riding 30-50 miles a day until a week before you leave, then a few 50-75 mile days loaded up, then break for a couple days before finally heading out. Honestly though, you're asking a lot of yourself. 100 miles a day is a lot when everything goes as planned; things wont go as planned. Not for six days.

I'm assuming you weren't fully loaded when you rode 100 miles last year? 100 miles loaded is more like 150 miles unloaded (or at least, it's going to feel that way). You need to get out and ride some serious distance with your full kit. See how it feels. Hit some hills. See what breaks. Sort out the new pains you're going to feel from carrying and handling extra pounds, while sporting the profile of a dumpster.

In general, the whole campaign sounds like a really bad idea. If I were you, I would totally do it.