Hi Jon, welcome to the world of caravans, now you've started something! You did well in finding this forum, it's just so usefull and user friendly, I wish I'd found it sooner.
I agree with Mel, you'll be wanting to ask a few more specific questions soon but I suppose you don't know what questions to ask yet do you. So dont jump into anything before you get some advice and there's no shortage of that round here.
The other thing is as Mel says, you need to hop in and out of as many caravans as you possibly can, they all just have such a different feel to them.
The weight of the caravan in relation to your vehicle is the big thing, I imagine you've read up on that by now. So then you need to ask yourself whether or not you need or want to change your car. Personaly I've got a skoda Octavia deisel estate and dont want anything bigger, thats a prioraty for me so all my caravan choices are gonna be based on what I can pull with an estate car( which is loads of choice)
The relationship between towcar and caravan is the big safety/ comfort factor in the decision. I say comfort aswell because if you get it right then the towing is easier on the nerves. (you need to enjoy the travelling as well as the holiday.
You'll hear people talking about 'the tail wagging the dog' This is when the caravan is wagging the car. Caravans can sway for a variety of reasons and this is what we all try to eliminate. Correct weight, carefully balanced packing, good stabilisers on the tow hitch, good servicing and thoughtfull driving technique.
So: get a van thats within your cars ability
get a good stabiliser.
And: don't forget that the caravaners number one enemy is damp,
be carefull of this if buying 2nd hand
Happy hunting.