Travelaround a no build build is a good idea. Getting out on the road will give you more thinking time about your plans
In the long run it will also help you decide which van builder will work best for you. It might even work to have 2 different teams. Just put one team on the insulation, walls plus basic electrical including solar and powered roof fans, propane and heater as well as any water and waste tanks. When they are done the other team comes in for installing cabinets and other fittings including sink and water, hooking up the heater, etc.
You do need plans drawn up and a schedule for the order in which each task will get done. Otherwise you will have chaos, missed deadlines and back tracking rework. Plus you need to know when you must order the various supplies.
There will be a number of weeks when the van will not be available for your use during the construction phase. So go and get some camping time in now.