Before diving in to nomadic living, it's a good idea to rent a van for a week or so to learn more about what it actually takes to live in a vehicle. If you're a little more certain, you could even buy a used van or RV with the intent to sell it later on. That way you can get a longer exposure to van life or RV life without the need to return an expensive rental at the end of the weekend or week.
The major downside is that renting a campervan or RV is expensive. But it is much less expensive than buying a van, spending time and money to build it out, and then discovering that life on the road is not what you expected.