@Alldigital have a search through here for some of the towing discussions, for the details. here is a link to one of the web pages with picture that may help you understand some of the terms used :
https://www.campsaustraliawide.com/caravan-tow-vehicle-towing-capacity/
The legality is up to you, with the figures being:
GVM - Tare gives car load capacity
2100 - 1480 = 620kg
Note that tare is empty car, no people, not full of fuel, no add ons, no luggage and must include the towball weight of caravan.
GCM in this case is GVM + tow capacity (3700 = 2100 + 1600) so unless there are other restriction with tow ball weight etc one does not limit the other.
Van payload or gross mass should be stamped on the van, if old enough not to have it, I am not sure of legalities.
The gross weight of the caravan cannot exceed 1600 for your car.
This means that the van payload can not exceed 1600 - 920. That is 680 kg.
Again note that Tare for a van is empty. No water, gas, added accesories, food, clothes etc.
Also note that the van (to be towed by this car) must be under 1600 and also under the gross trailer mass (GTM) stamped on the van (if it exists). So if the GTM is lower than 1600 than you need to be under that value. If it is over you can not go over 1600.
Also note the requirement for brakes in your state. I suggest that you use the diagram in the link and written in the details and do the calculations. This will help you determine the legalities and margins that you have.