The Camping and Caravanning Club produce this list - although don't start buying until you see whats in the deal when you buy the van (You may get a 'starter pack' thrown in by a dealer, or a lot of kit left by a previous owner.):
Camping and Caravanning Club Blog - 20 things you need in your essential caravan starter kit
Just at the moment there is a shortage of new or used vans because of covid and many dealerships are very low on stock. If you are new to caravans it might be best to buy from a reputable dealer with some warranty - however if the right van comes up you can always employ a techie to check it over for you - especially for the dreaded damp!
- a list of over 500 here and if you scroll down pre-purchase inspections are one of the headline items:
Approved Touring Caravan & Motorhome Servicing in the UK (approvedworkshops.co.uk)
Start with the kerbweight of the car and provided there is no lower limit specified aim for about 85% for the MTPLM of the caravan. This is an area fraught with debate and you will find a current posting on this forum if you wish! Then look at layouts that fall within your limits - handy reference file at the back of every PC magazine of new vans to get you started.