Greetings & Welcome!
I have to totally disagree with adding windows later, they should come first so you can build proper frames around them.
Make sure you get opening windows, so you can avoid roof vents. You don’t want any added holes in your roof it’s at all avoidable, because sooner or later they always leak.
One of the best schemes I’ve seen used two different types of tip out windows. On on side, the windows tipped out at the bottom, and on the other side, only the top half tipped out. Both were reasonably rainproof, but the combination allowed natural convection cooling without the need of a fan, making them extremely energy efficient.
The more windows, the better the ventilation, and the view. Most experienced full timers have switched to window vans. Cargo vans are a newbie mistake, but they’re heavily promoted by people looking to profit by recruiting others, because they cost so much more to convert. The promoters make big money off from solar panels, controllers, expensive batteries, roof vents, expensive heaters, 12v compressor fridges, and gym memberships, all of which are questionable choices at best. The best builds don’t incorporate any of them, because there are many better and cheaper options available.
These promoters neglect to tell their victims that they are likely to lose most if not all of the time and money they put into converting cargo vans. Adding windows does greatly improve the resale value though.
For less than the cost of a month or two of gym membership, you can have your own toilet & shower which is so much more convenient. Simple systems are better, the less you have that can go wrong, the less that will go wrong.
"I can live like a king because I work like a dog." ~ An anonymous vandweller