Hello Shona,
Sorry to have to point out that as you say you are new to caravanning, I do wonder if you are subject to the limitations imposed by the change of driving licence categories that were made for drivers passing their tests after Jan 1997
If the driver passed their test after 1997, then they will only have cat B (for normal cars and towing) This limits you to a combined Maximum Authorised Mass (MAM) not exceeding 3500Kg. If you passed your test before Jan 1997 then you will have Cat BE which allows a much greater combined MAM that will cover all UK cars and caravans. In essence the combined figure is the sum of the car and caravan MAM's
The Maximum Authorised Mass or MAM of a vehicle is highest mass (Weight) the manufacture allows it to be, i.e. fully loaded. It is a fixed figure. The same applies to the caravan so the MAM is virtually the same as the caravans MTPLM figure.
As you are considering the Sorrento, most of these have a kerbweight of about 2000Kg, so the MAM for the car may well be nearer 2800Kg. You would need to check the exact figures for the model you are considering, but that would mean you could only look for a caravan with a MTPLM of about 700Kg - Not a realistic proposition for a 4/5 berth.
The Sportage seems to have a kerbweight of about 1500Kg which means its MAM will be about 2200Kg (again you would need to check the exact figures for car you are considering) so that would leave you with about 1300Kg for the caravan's MTPLM. That is a more realistic but still tight proposition.
Don't forget that this limitation is based on the MAM's for the vehicles not what they actually weigh.
If you only have the Cat B licence, you can take the towing test and convert your cat B to B+E which gives you the wider range of mass limits of the pre 1997 Cat BE.