Did it at the
start of June, although I'm probably not the best person to ask about essential stops as I did it in a oner. That should give you an idea of how challenging the riding is, but just be aware that there are some very sandy sections between Thetford and Kings Lynn. Also, be mindful on the drop into the bottom of Castle Acre, as there's a ford with a massive drop off into reasonably deep water, take the bridge on your left.
Some ideas though; don't bother doing the pointless loop around King's Lynn centre, don't go down to the front in Sheringham unless you like dodging tourists and cars with zero spacial awareness, and buckle up for the transition though Norwich, utterly hideous if the traffic is even remotely heavy.
There's places to stop and grab food every 30 to 50KM or so; petrol stations, supermarkets (both big and small), cafes, pubs, chippies, marinas, stately homes, etc, etc. Not all of them are directly on route, i.e. the SPAR and chippie in Castle Acre; but you go through enough built up areas, with enough regularity, that you don't need to carry much extra food or liquid. This also means there's also plenty of places to stop and have a mooch about, if that's your thing. Plenty of woods and field edges to pitch a tent, or chuck a bivvy bag down.
I had a very nice ice cream at the Granary Stores, Ranworth Staithe, which is on Malthouse Broad, proper sorted me out for the run to Diss.
