I’d second Streatley for over night – it’s a YHA rather than a YMCA, so popular with walkers doing the ridgeway and the thames path.
Wallingford has it’s annual folk and music festival on so accommodation in town is likely to be all booked out.
The great thing about the Ridgeway is it passes near a lot of places, but not through them…so you have to come off route to find towns/villages.
Did Wallingford to Avebury last friday and for four hours didn’t see a single other person..
You can’t really go wrong with most of the route – it’s pretty well signed, but take a map as well as there’s a few confusing bits. eg crossing A34 at East/West Ilsley.
Camping might be good option – plenty of places to wild camp.
There’s detail online somewhere about where water taps are on the route which is definitely worth noting.
Enjoy!