On the topic of tow vehicles, don't just look at the power output of the towcar. That's important, but weight is even more so. There's a bunch of legalities that you need to be aware of (Caravan and Outdoor life give them), but I've also found that although my rig is legal (wrt weights), and the car is powerful enough, it would be ideal if my car was 100kg heavier. Simply because the heavier the car in relation to the van the more stable the rig will be.
Also, get a stabiliser. I use a Tando, but the yellow-blades are also reputed to be pretty good. I've towed with and without using it (over short distances) and there is no comparison. Especially if the wind is blowing. Wind plus unstabilised van equals very slow progress and white knuckles (or smelly knickers...).
As others have said, there's no-one better able to comment on what you want to do than your local reputable caravan and camping shop (generally, if it's got a Campworld attached, it's pretty decent - but the best reputations in the Country belong to Kennis Caravans in Roodepoort/Krugersdorp, Loftus Caravans in Pretoria and Tygerberg Caravans in Cape Town).
In terms of the law, the gross (fully laden) mass of the caravan (with its own braking system) may not exceed the net (unladen) weight of the tow car, (whether the van is loaded to the max or not). Aditionally, the gross mass of a trailer (up to 750kg and without its own braking system) may not be more than half of the unladen mass of the tow vehicle, even if the trailer is empty. The gross mass of the van or trailer will be that as stipulated on the chassis plate.
As Orange has said, it is better that the tow car's unladen mass is fairly heavier that the van's gross mass as this will benefit you in terms of towing stability especially in cross winds, over taking trucks etc.
As also said above the best bet is to buy from a reputable dealer. They will make sure that everything is in good working order, esp brakes/electrics/gas lines etc.
Good luck in your search.