Big welcome to the forum and welcome to the world of caravannnig, the stress is about to start :lol:
So You will need to consider [ just as a start]
The type of driving licence you have, this will give you the weight of caravan along with the weights of your tow vehicle you will be legally allowed to drive.
Are you going for new or second hand? Lots recommend second hand to start as if you dont like it you wont loose a fortune as you could just resell the van.
Good luck.