jekkyl – a cursory glance at the map would suggest there’s no camp sites in the vicinity. I don’t camp so haven’t a clue and I believe, but not certain, that the youth hostel closed down.
Wild camping would definitely be a risk and perhaps not a sensible one. Probably the best thing to do is research camp sites first of all.
As regards what’s interesting, close together are Wayland’s Smithy (long barrow), Uffington Castle (hill fort) and the Uffington White Horse. Also there is Ashdown House that definitely used to be open to the public.
On the other hand, the start at Overton Hill means that opposite is the West Kennett long barrow then Avebury is close by as is Fyfield Down that has the best preserved Grey Wethers.
There’s loads of tracks that run off the Ridgeway, ie plenty of gallops around Lambourn so that means springy riding!
As I said above, checking where the camp sites are located would be a good starting point.
I feel quite envious!