Hard runway, parking in good condition (no potholes or tall grass or rocks).
Of those listed, the only ones I recall having been to are Welshpool, Norwich, Wellesbourne, Sherburn in Elmet, and the 1st would have too little space IMHO, and is also very risky w.r.t. weather.
Norwich would be ideal but at £50 (?) is perhaps too pricey for most here, unless one can do a deal with one of the flying clubs. When I went there ~2 years ago I went to one of the flying clubs and it was about £15 which is totally reasonable.
Why waive landing fees? Is everybody going to spend £10 on cakes?
How about Cambridge? Or Shoreham? Or for a really exclusive get-together, with no risk of exposure to civilisation, how about Lydd?