I think you're overcomplicating the build. Everything you needed to travel for a month fit in a pair of panniers and a tank bag! Take the same approach with you van. Just add the elements your used the hotel for (eg. bed, toilet, power), keep it simple and hit the road. You'll learn what your needs and wants are with experience. Address them as they arise. To do otherwise is just guessing, potentially wasting money and time.
You'll discover what's important to you as you travel. My initial plumbing was very simple. Over time, I grew to dislike washing my hands (or dishes) in ambient temperature water. So I eventually addressed this by installing an instantaneous hot water faucet. Ditto with my desire for an inside shower. Ditto with my diesel heater.
For some folks, solar is essential to their use case, while I think its suboptimal use of valuable roof space, even though I have fairly high power needs. Some folks dedicate a lot of space to cooking inside their rig, while I like sampling the cuisine at local eateries and heating up leftovers in the microwave in my mini kitchenette.
No one (including you) can tell you the best layout or amenities for your build more accurately than 6 months experience on the road will do.