To while away a few hours, open Google maps - search 'Caravan sites near' your preferred destination, and it will show many sites in the area chosen and links to websites on the screen left. I suspect that most newcomers will join one or both clubs for access to their main sites and private 5 van sites known as CS or Cl listings.
Consider the cost of all the items you will need - a dealer 'starter pack' would be a big help - after all the typical aquaroll and wastemaster are about £100 to stat with.
For caravan insurance, depending on what van you purchase, you might be able to insure for market value, agreed value, or new for old. Both clubs offer insurance products and there are others listed in PC Mag. I personally have Caravan Guard' over many years.
At the mo I suspect your hunting will have to start on-line, depending on where you live visit the website of local dealers, most will carry new and used for sale with many pictures of the actual vans.
AS above decide what weight you can tow, how many berths you need and what layout you prefer.
Good hunting!