Getting the train out to Stowmarket on Friday afternoon and then around to Kings Lynn to get then train back to London on Tuesday. Looking to cover around 40 miles per day and camping overnight. This is the route i have planned without knowing the area at all. https://cycle.travel/map/journey/75109
Do you have any suggestions of how it could be improved or things/places we should do/see along the way?
Mile 6 - continue forwards to Mendlesham to cross the A140 (which may be very busy) in Brockford Street for the minor benefit of a 30mph limit and turning left off the A road, instead of turning right off a 50mph stretch in Brockford Green.
Mile 20 - very debatable but I like Brockdish and Harleston so I'd go through them despite it meaning you have to pick two of a choice of annoying crossings of the A road.
Bungay to Cromer I don't know on a bike well enough to comment.
Mile 83 - I'd go through Felbrigg Hall's grounds if it's open (the northern branch of Regional Route 30). The surface is that yellow gravel on top of tarmac that the NT likes. It's shorter, more scenic and the cafe is good. Maybe a couple of cattle grids and some speed humps.
Mile 89 - if you like old trains, it may be worth the 2 extra miles to detour up to Weybourne and back, riding past the well-preserved NNR station and maybe see a train.
Mile 102 - your route past the back wall of Holkham is fine and fast but you might like to consider detouring north on back roads to Warham and then parallel to the light railway to Wells-next-the-Sea harbour, as mentioned above. I wouldn't bother with the sand tracks that Route 1 uses unless you enjoy that sort of thing. Then the road west from Wells Community Hospital is passable by bike (some macadam, some tarmac, some cattle grids) to rejoin Route 1 on tarmac at Holkham Hall and south past the obelisk, although the more direct road west to join the B road into the Burnhams is also open to cycles and would mean the whole detour adds no distance (but probably some time because Wells will be busy with tourists!).
After that, the route is well-known and I think quite good fun, a good intro to the area even if it doesn't go through as many places as it could. I think most if not all of the pubs on or near that stretch are fine, at least until Lynn town centre
Burnham Deepdale (I think it's called Dalegate Market but it's been a while), Titchwell (RSPB) and Thornham Deli are all good cake stops and riding the long roads down towards the coast can be fun - dragging back away from them, less so, but easier after cake!
Hunstanton, Heacham and Snettisham are all good beach detours if you have time, decreasingly touristy.
As you reach the top of the drag out of Ingoldisthorpe, look back right over the fields and across the Wash and Boston Stump is visible on clear days.
Sandringham is famous and magnificent but if you're too late for it to be worth paying the relatively high entry fee, the loop north and west from the visitor centre (called Princess's Drive or the Scenic Drive - motor traffic has to go clockwise around it) can still often be lovely.
Then the final half-freewheeling from there into the Woottons and the old railway line to the Walks is a lovely ride, but keep one eye open for tree root ripples alternating with very very smooth tarmac as it passes over different council and drainage board territories.