Enjoy the London to Brighton, Stap
Mrs Geez and I have done that a few times, on singles and tandems - and found it really tricky on the tandem. Too many people, too unpredictable, leaving too little space. Lots of forearm muscle strain from covering the brakes! And the biggest problems on the climbs, especially on Ditchling Beacon when the road is full of walkers and pushers, hard to keep a slow moving tandem upright.
The last few years we've done the Hampton to Hove instead - similar route, far fewer people and more regular cyclists. I'd recommend it. This year it's July 13th, I think