As others have said, we are all different in terms of what we can and will tolerate. Personally, I would never plan to include 6 hours of rest on Saddle Sore, it's way too much and if you're properly rested when you start the ride, should not be needed.
If you set out to do a Saddle Sore, and don't make it, you WILL be disappointed. Exactly HOW disappointed is up to you and I suppose, by how much you fell short.
I seem to recall that you could get a 'special' cert - or at least an immediate one? - if you do a SS1K to Moonshine per their rules, so it is an attractive carrot, no doubt, especially for a first timer. But your safety and the happiness of your marriage should be considered as well. If you plan to do this ride in April, I consider heated gear for both of you non-negotiable. And figure out how you're going to power it. I rode my husband to Romney, WV from Baltimore on March 9th a few years ago and it was a bit chilly. We found that we could not run both sets of heated gear at the same time due to the limitations of the FJR's alternator output so we had to take turns. I think it was about a 3 hour ride - you're talking much much longer. No way we could have done a Saddle sore that day and remain married and/or both of us among the living. I've done quite a few long days in the saddle, I can man up when I need to, but riding long periods in the cold will have a negative impact as an experienced voice described previously in this thread.
Just another option to consider, and I believe it is sold out this year, but the IBA has a dinner in Jacksonville in March and a SS1K is offered there as well with a special cert and immediate receipt of it. I've not done the ride offered in Jax, but the folks who do it sure seem to be very happy with the ride. Jacksonville/Florida in March sounds much more attractive to me than the ride you described, but that's just my opinion! Also a great crowd of IBA members to mingle with in Jax!
As others have said, only you know the bounds of the limits you two can ride together. Actually, you don't know that, that's why you're attempting this! But seriously, these are very personal decisions. You are going about it the right way though, asking questions and for information. Just remember there's some experience talking in this thread and just about everything I saw looked like great advice for a first timer.
Bottom line, I wish you all the best on your ride and I hope you are successful! Even if you decide to make the attempt another day.