Route:
Ended up doing a modified BHF route with most significant changes on the way out of London and avoiding Haywards Heath.
Best stretch of cycling was between Nutfield and Smallfield. We ate up the miles very quickly on that stretch.
Roads around Crawley Down and Ardingly were pretty terrible.
Lessons learnt:
If I do this again the future, I will definitely follow the cycle.travel route more as already suggested on this thread.
Climb up the Ditchling Beacon was painful. Ended up walking up more than half of it. Definitely should've have trained more or come up with an alternative route.
Most importantly this ride taught me a lot more about my bike than any previous ride;
Pros: learning to time gear shifts better to ride more efficiently, being more patient on hills and appreciating lower gears with higher cadence
Cons: wishing I had bigger rear cogs for climbs, wider tires for comfort
Others:
Met some very nice and helpful locals on the ride down who looked out for us.