You will notice the route guide has a star-rating. That's intended to be an easy way for esp parents cycling with kids, but also less-confident cyclists to get an idea about a route.
Check the route guide before setting off, as it also includes a weather forecast!
@WilliamNB it navigates through Guildford without using busy roads too
@WilliamNB or for the more intrepid, ride the Thames Path from Central London to Weybridge, then go down the Wey Navigation to Guildford before picking it up.
There's a few rougher bits around Send but passable in the summer even on a road bike if it's been dry.
I did it last year from Hampton Court Bridge with this route: https://www.komoot.com/tour/594728390?ref=aso&share_token=a1FMB1A6rU0mRWUQa7gvIFUK9q74HhMwCtJ3NwXtRBgve2h3Zc
Also don't forget the Ice Cream cafe on Shoreham Beach!