This is our dream as well but currently baulking at the cost (£750,000 plus including decent accommodation) unless we look at moving to Wales or Scotland.Having also recently purchased a motorhome for the winter months (I know, I know), there is definately an opportunity to make good money outside of the core months as many are close and there is still demand.
We would look for plenty of 16A hook up and watering points
Spacious and clean toilets and showers with sufficient areas to dry yourself without bashing your elbows or getting all your clothes wet. If you are building from scratch worth giving a lot of though to the design and specification of the amenity block i.e easy to wash down, robust cubicle design (i.e tiled blockwork v compact grade laminate partitions, shower curtains v cubicle doors etc, etc)
Easy access to local transport
Well marked spacious pitches
Provision of local guides including pre-printed walks and cycle rides
Alliances with local business are always good, ie discount vouchers, delivered curry/chinese and pizzas etc
Some hardstanding areas for the winter months
If you have the space, a couple of fishing lakes as a draw (we've been to 3 sites this winter which had lakes and all were busy), dog walking area, childrens play area and a shop.
Pricing strategy is obviously important depending on the target market and facilities provided. We have been paying anywhere between £10.00 for a C&CC CS site to £28. We don't mind the Ryanair approach of charging extra for awnings, showers, dogs etc as this approach does allow you to disinguish between clients different requirements i.e some tenters just need the basics, others need everything, some all year round motorhomers who want everything and others who dont because everything is on board.
Good luck