Lots of lovely bits but I don't fancy the bit from Strood to Gravesend, and probably on from there.
I'd be inclined to either:
turn right from Strood to Wainscott / Chattenden / Upnor and approach gravesned via the back roads (I used to live round there when I was a kid and cycled round all those roads way back when, but it's a lot busier now...)
turn left before the Medway towns and avoid them altogether, crossing the Medway on the Motorway bridge cycle path and going on the lanes via Cobham / Sole Street, etc.
Lots of lovely bits but I don't fancy the bit from Strood to Gravesend, and probably on from there.
I'd be inclined to either:
1 will add distance, 2 might reduce it.