Budget?
Desire to travel (annual anticipated miles)
Need for comforts vs. cost (RV vs. camperized van
Ability to build the van out (or access to help)
Ability to repair mechanicals (not needed if flush with $)
Timeframe (1 year, more?)
Yes for a family of 3 you will likely want bigger vs smaller, like a euro tyle high roof, long wheelbase, or similar. If you have the budget for it, that's likely your starting point.
Many threads exist on Dodge Promaster, Ford Transit and some on MB Sprinter, just search, you might find the search easier on Google vs. this forum, as the Google search brings up our forum posts as well as Reddit and others.
Watch YouTube camper van videos to get an idea of the inside sizes and what families are doing.