I'd suggest short breaks for a little time off the bike, maybe 5 mins every 20 or so miles, but not so much your legs stiffen up. On organized rides, I often wait until the end to eat lunch, as it is part of the event, and included in registration cost. I usually wait until after the ride to eat a meal, but bring a lot of snacks and drinks for the ride. Hydration and fuel is necessary on a ride of this length. It is also a good idea to bring something you are used to, so no surprises with indigestion or otherwise.