Always go for the biggest, if your van is plated at 3 ton (won't quibble about 6 kg ) then you can rest assured when your packed up and going away you'll be close or over that mark especially if the builders tare weight is wrong....
............I would be looking at 3500kg tow cap minimum. I don't want to get into the weights debate again. Your tare is empty van, thats no gas, no water, no nothing which doesn't leave you a lot after you've added gas, water and tucker, not to mention the big box, 4 pushies etc.................you can be anal and do the weigh bridge thing every trip but that would mean not only checking that your van complied to it's plated info but your tug does also, many would get a shock if they put their loaded tug on the scales, 750kg carrying cap soon gets eaten up with bodies and all the junk you throw in the back.....................
So go for a 3500kg tow cap, if you go a dual cab, get a tray back just so much easier to load and get at your stuff, canopy cheaper than tub jobs.
Have a good look at the compliance plate............it's probably wrong.
Also highway pattern tyres on your van will do a better job, less problems and last longer than some macho off road tyre which will chop out more than likely, no need for fancy 4x4 rubber, it's a lazy axle, it doesn't work just looks cool.