What Van is it? :D
I've wanted to do something like this for a while, also toured in vans and traveled a little in campers. From what I've researched you'll constantly be rebuilding and adjusting different aspects as you go and learn what works best for you. Your plan/layout looks reliable and what most of the commercially setup vans run.

Probably most important thing I've learnt from YouTube builders and articles is to use sealed materials when building to avoid moisture and in turn mould! Which can make you really sick. So like timber lined walls are a no no even though they look so nice. Unless you want to go through the trouble of properly sealing both sides of the wood.
And in turn ventilation is important - I've seen exhaust fans be installed in the back in the roof - and then they crack the front window (they have those plastic wind deflector so it hides the open window) for fresh air in and humid air out from the fan. (Hopefully makes sense)