The interior width of the NV200 is 1.5 metres, I figured on a side unit of 40cm and a bed width of 110cm. The cooker is 40cm deep too. I wanted a cooker with an oven if it all possible as it gives you far more options when cooking than a simple 2 ring burner. I must admit it was a challenge to fit it into such a small van, and the place I eventually chose was pretty much the only place it would fit. As it turned out it works very well, as you obviously need the door open when cooking and even opening it an inch or so gives enough ventilation. The cooker is an old Eastham Maxol caravan / boat cooker. It’s mounted on a simple base and fitted to the sink unit with bolts and wingnuts. It takes a couple of minutes to remove.
You can buy new models of a similar size such as this,http://www.norfolkmarine.co.uk/shop-online/voyager-4500-burner-oven-grill-cooker-grill-p-23205.html It’s pricey of course, I paid £20 for mine -one taken from a scrap caravan and fortunately it works perfectly.

If you want a cooker that you can use outside and still have an oven this Camping Gaz model seems good. 
https://www.campingaz.com/uk/p-26652-camp-stove-oven.aspx
Costs around £200.
I didn’t want to use a big gas bottle so I use this, instead.

It’s small enough to fit under the cooker unit and you can turn off the gas when traveling or easily remove the cylinders completely if you wish. (Accessed from outside with the door open!). http://gasproducts.co.uk/cadac-dual-power-pak.html
The cooker unit in my van is NOT a permanent fixture it can be easily removed and used outside if camping or removed completely if the seats are put in. A proper permanent campervan conversion will require a sealed gasbox with a fixed regulator, floor vent etc. You should of course consult a professional for any gas fitting.
Of course we always cook with the door open and have a CO detector fitted, I prefer this type,

As you can get a reading at any point and see what the level is, it also saves the peak level, so you can check that you’re not getting anywhere near the danger level. There is a danger of fire as well as CO poisoning so you must watch the cooker constantly when cooking, Having a Fire Blanket and Extinguisher on hand is advisable and it’s also wise to have a first aid kit in the van.
The sink unit was fitted first, I used a Smev VA930 sink which is 28cm by 38cm, I made the cupboard from 15mm laminated chipboard, you really should use ply but I’m a cheapskate! In any case I wasn’t 100% sure it would turn out O.K. and it wouldn’t cost much to do it again. I made it 1 metre wide, there was just enough room to keep it in situ with the seats replaced and the cooker would fit at the side. With this layout there is just about enough room to squeeze in and out of the side door, but if I redo the sink unit I will reduce it to about 92cm wide to give a bit more access room. UPDATE: I have now remade the unit a little shorter and it has helped access a lot. Waste water tank is an old 20L car wash chemical drum, fresh water is 2 x 10L barrels, they have to be food grade so no old chemical drums for those! I used some that had been used for syrup. I keep one full as a spare and swap with the other when it runs out, not too heavy to carry. Pump is a standard 12v immersion pump.
Tap is a Reich single cold water tap.

There was only just enough room to fit the pipe to the tap when I fitted mine but I was stuck with the tap hole already drilled in the sink as I bought it secondhand, If I was fitting a new sink and tap I would fit the tap to the worktop rather than the back of the sink. May also use a manual pump too such as this, 
Saves wiring and load on battery, also gives you more control on dispensing water, 12v taps are either on or off, very little control of flow. My tap and pump plug into a 12v socket so I can remove easily.