Ah yes, if you haven't been doing it regularly, four hours is a long time in the saddle! I'm currently way out of shape for such an endeavor, but years back I did longer rides pretty often. I found, especially after a winter off, that I had to work up slowly to the long runs. That was partly to restore conditioning, but also to get the butt used to the idea. There must be 1000 different seats out there, apparently one size does not fit all. So far my hands bother me more than my butt, in fact I just added short bar ends to my straight bars to facilitate more hand position changes.
Telephotos might be problematic, but there are a lot of 35 mm P&S cameras that actually take decent pictures. And I can fit my Perkeo II and three rolls of film in a Tamrac belt pouch I have.