The insulation is rarely sufficient if you want good insulation. In most cases, the old fashioned pink fiberglass insulation was used because it's easy to stuff in to the openings rather than having to cut polyiso to fit.
A lot of people who start off with the conversion vans end up ripping the entire interior out, partly because it's space consuming - you lose as much as 6" on each side wall as compared to, say mine, where I lost less than a half inch each side with the finished wall surfaces I used.
IMO, there is no point in paying for a finished interior if you're going to remove most of it anyways. The fold down beds in the rear are notoriously uncomfortable to sleep on and ruin any storage beneath it because of the mechanics of the bench seat.
Also, keep in mind that most of the conversions are what's called a TV top. It does not give even a 5' tall person standing room. I have a 24" high top and have a 6'2" standing height in mine.