Water is always good, so is shade for those summer months.
If I were you, I'd be looking at somewhere north of Gloucester, on the river...
Clean and bright amenities are a bonus too.
Flat, or relatively level sites are good.
Clean potable water (filtered) not river water as it can make unsuspecting people sick...
I agree with the options for groups, as I've seen groups setup, with sleep tents, food tents plus the outdoor, under cover kitchen, kiddies pools etc..
Many moons ago I had my own business, my Public Liability for $20mil plus Professional Indemnity was around $3500 p/a, so expensive, but too bad in the scheme of things, and is absolutely essential.