Hello Dave,
I started to reply using a tablet, this reply has been edited:
Welcome to the forum.
I'd like to amplify some of the points already made:
As you already have the tow car, it's important to understand its limitations. The limits are particular for each model of the car, so you do need to be precise about the make, model, body , trim pack and engine. VW will often use the same size of engine, but offer it with different power outputs,and that tends to alter the maximum towed weight figure for the car.
By all means use one of the tow matching websites, but do check they are referring to your exact car and caravan and the figures are the same, near equivalents are not necessarily the same.
As others have picked up on is you stated 3500kg limit, I presume this means the driver does not have the BE or B +E on their licence. You need to understand that the wording for the B entitlement which uses the phrase "must not exceed a combined MAM of 3500kg" what this means is you must add the cars MAM (Same as it's Gross Vehicle Weight) and the caravans MAM (Same as it's MTPLM) together and the sum of these must not be greater than 3500kg. This is a paper exercise, so the result cannot be changed by reducing what you actually carry. The law is black and white about this with no latitude.
The car does have legal limits, and they are stamped on the cars weight plate, You must not exceed the cars Gross Vehicle Weight or the Gross Train Weight.
The towing ratio is also a paper exercise which takes 100 X (MTPLM/Kerbweight,). It's a worst possible case scenario.
The UK caravan industry recommend novice caravanners do not exceed a ratio of 85% and experienced caravanners should not exceed 100%. These recommendations have no legal power, but they are a starting point, and are based on the premise that caravans are not easy trailers to tow, their size and weight do impart some considerable additional forces and loads on the car, which the car has to be able to control. Ensuring the car is always heavier than the caravan is seen as an important factor to help with towing. Regardless of the industry guidance you should never exceed the maximum towed weight limit set by the car manufacturer.
If you have not fully decided that caravanning is right for you, it makes sense to look at second hand caravans. The bulk of the depreciation will have taken place and most of the new product* niggles should have been sorted. It also means that if you do decide its not for you you will not lose as much when you sell on. - Some people actually make money!
How to buy? Always work out what you want before you agree to purchase. Ask lots of questions, I’d also suggest you keep a written list or video the process. Ask open questions that makes the seller tell you the whole story, e.g. Don’t ask “Is the caravans dry?” Ask “Whats its water ingress history? “ If any answer seems anything less than cosha walk away.
Take a knowledgeable friend with you. Their experience may offset any shortfall in your own. If second hand, do use an independent engineer to check the caravan over before you agree to purchase.
Where to buy? If you need the confidence of having a formal warranty use a dealer. You will pay more ( the dealer has to make a profit) In law dealers are expected to use their specialist knowledge to help you, they are obliged to answer any questions you have honestly.
If you are looking at a private purchase, it will be cheaper, but it won’t include a warranty, and whilst the seller should answer honestly, there is always that possibility they may not be as open as they should be. If anything does go wrong, you technically have your rights under the CRA, but it is more difficult to bring the seller to book.
Others will tell you their likes and dislikes concerning layout and features but ultimately only you and your family can choose.
Good luck.