Yes Mireille you have made the right choice if you want to do some sightseeing in and around London. Windsor and Eton is not too far away, Windsor Castle is a day out in itself as is Hampton Court Palace, again not too far from the Chertsey site.
The site itself is not far from the M25, it's behind a car sales garage and it's bounded on one side by the River Thames. It has the usual C&CC facilities with a barrier entrance so your caravan is safe when you are out and about.
When we visited the site in March 2005 it had recently been redeveloped and the grass seed hadn't yet grown but I'd imagine that it is nicely grassed over by now. You might need to take two ehu leads unless you are on a full service pitch, the normal cheaper ehu pitches were a long way from the bollards but this might have changed by now.
In Chertsey itself there are shops, takeaways and pubs and some of the pubs serve relatively inexpensive meals, there is a large pub a short walk away across Chertsey bridge which serves food.
There are wild parakeets in the trees around the site, the only slight criticism that we have is that the site is under the flight path for Heathrow airport and the aircraft noise can be intrusive at times but you'll soon get used to it.
We would go to Weighbridge railway station to go to London Waterloo, a short tain journey away rather than having to pay congestion charges and worry about parking the car in central London. ( parking is free and congestion charges don't apply at weekends, a good time for evening theater visits)
I can't remember the exact details now but we bought some sort of off peak saver tickets which allowed us to use local trains, buses and Underground but I can't remember if they were daily or weekly.
They were a great bargain as we did a lot of sightseeing from the top decks of buses but the best thing was that these off peak transport tickets gave 2 for 1 admission on most of the major tourist attractions, some theaters, the Tower of London, London Eye, Thames boat trips and many other things. The staff at Weighbridge station put us on to these tickets, they more or less paid for themselves in the savings on other admission prices and we never had to worry about finding change or fishing wallets out etc.
I'm sure that you will enjoy your stay at Chertsey, it's definitely on our 'to be revisited' list.