Don't know where you live but there are many caravan specialists, we actually have a caravan for sale 4/5 berth, end shower room, bunks £4,500
When buying a caravan you want to make sure its not damp, you can buy a little probe thing (very technical) we take ours along with us when we are looking at caravans, never trust somebody that says their van is totally dry, unless of course it is relatively new!
We store ours at a local farm, you can get secure sites in compounds with security cameras etc depends on how much you want to spend, farms can charge £35 - £45 per 3 months, but most secure holdings are £25 per month, only other option is on your drive or in your garden, you can get posts that you cement into the ground and as long as you have a good wheelclamp and hitchlock you shouldn't have a problem!
Sorry going on a bit but I love my caravan and the holidays it gives us. Join the Camping and Caravan club, they give you a brochure of all the available sites and their facilities etc.
You can look on motorhelp (website) or look in ad-mad or Auto magazines you'll find bargains everywhere at the moment, but it is best to buy from a reputable company though, they give you guarantees aswell for a year. We bought ours from Lowdhams (they are on the web)
If I think of anything else, I'll post you. But mainly, take your time looking at different layouts, see what suits you best, and enjoy looking. Some companies let you hook up and try on site before you buy (I know Lowdhams do)