Are you local to the N sea. Part of the UK route goes close to me in East Anglia. The official route is well selected using a lot of local knowledge.
For the UK part, note that Sept is excellent touring weather but the conditions can break in Oct with gusty Westerly winds and heavy rain , worse the further N and W you go.
Wild camping is possible but is not strictly legal. You can camp in YHA grounds and many farms let you have a patch.