A good way of working out how to make things work was to see how others had done it, and how the parts worked. The following sites and resources may be invaluable to that end:
The other way to learn how things work is to take them apart. An well-loved donor touring caravan is an excellent source of cheap parts for a motorhome and also to discover how components work together in a mobile living space.
Finally, you should spend a fair bit of time looking at both professional van conversions for sale on Autotrader and Gumtree, and at the pictures on the Wicked Campers site (last time I was in New Zealand I rented a camper from them for a week, which partly inspired the end paint job – or lack of – and there’s a gallery of some here).