hi Ul, have fun riding these shakedowns. All the best with the B17, I am pretty much convinced that warmer temperatures will help with it forming to you quicker, but I hope it is reasonably comfortable for up to an hour at least for now, thats how mine was for a while (and the used one I bought recently is similar as I have it on my bike now on an indoor trainer, and tend to do 45 to 90 min sessions on it)
as for weight, you know, at first I thought it was a bit much, but then going over your list, I saw that you have essentially the same amount as I always have on a trip----but, now, with the electronic doo-dads, the phone, D40, laptop etc means that your 48lbs is probably "X" amount more than what I used to have, but all the electronics and chargers.
In any case, these rides will be good to see how you like the weight distribution, I personally like a lighter front end, and while I initially thought your front rack was way to burly, I see with the extra electronic stuff, you probably do need the extra upper rack part of that front rack.
going back to the saddle, I would suggest also keeping a real eye, ear?? more like "feel" out for how it is, and perhaps making some small adjustments with it to see if it would be more comfortable.
back to gear--I would find 3 spare tubes a lot, a tire? dunno, I was never one to carry a spare tire--as you can see, I am generally pretty darn careful about my total gear weight and while I forget exactly what weight my stuff used to be, I am fairly certain it was around 40 lbs (again, this makes sense if you subtract tire, 2 spare tubes, and all electronic stuff)
oh, as for fenders, I find that they make a real difference for keeping crap off the front derailleur, and your feet too.--*oh, no rain pants and rain botties? I wouldnt tour without either. In my opinion, wet shoes take so damn long to dry, and wet feet suck big time, especially if you are run down a bit and if its the least bit cool. I find these indispensible: