Similar reqirements here in NL to register as a camper.
A minimum internal height of (from memory) 1.73mtr over a length 2mtr X 1mtr wide, can also be a poptop, on some types of vehicles 1.73 X 1 X 1mtr.
Cooking facilities with work surface, sink with water supply, storage facilities, sleeping for minimum 2 people, seating for minimal 2 people in the living quarters, seats can be converted to beds. Table which may be removable.
There are minimum size requirements for the beds and height requirements for cooking /work surface and sink.
Don't recall there being requirements for windows or a fitted awning bar, and stickers definately not......

After conversion the vehicle has to be re-registered as a camper with the vehicle registration authourities and then you have to seperately re-classify the vehicle with the tax authourities, which I'm given to understand tend to be more..er..difficult.
The advantage of re-registering as a camper is the difference in road tax, at present you pay a quarter compared to a regular private van (commercially registered vans pay even less).
The government are attempting to increase the road tax by 50% for campers and motor homes.
At present I pay around €147.00 per quarter, if it was registered as a private van that would be around €588.00 per quarter. (or €588.00 per annum compared to €2352.00 per annum)
Rates vary depending on engine size, type of fuel, weight and region/province. I have the misfortune of living in the most expensive province.
Tax on petrol vehicles is cheapest but petrol is generally the most expensive, tax on diesels is more expensive but diesel is cheaper than petrol, tax on LPG vehicles is the most expensive but LPG is cheaper than petrol or diesel.
There are some more finer points but that's the general requirements.