There are lots of options for insulation, but I live on an island with only a few. These seem to have worked well for me. They were easy, cheap and the difference was immediate. You can over think this, in my opinion.
The floor liner came with the van and it's great. I keep thinking I need to add baffles and drains, but so far the problem hasn't presented itself, and I've dove out of the van a lot. So far, I just have the dehumidifier. My towel, bathing suit and t-shirt are mostly dry by the next day. No stink, which is the most important thing to me.
Here's a conundrum that has come up. In my Sprinter, the cargo area was hard separated from the passenger cabin with foam insulation and fiberglass. On my Transit, I have kept this open, with only a shower curtain to give a bit of privacy when I am changing and whatnot. There is no question that my Transit is normally quieter and a lot smoother than the Sprinter... until I hit a bump or uneven ground. Then I hear all the hanging stuff swing back and forth. No, it's not that bad but it's part and parcel of the trade-offs I have had to contemplate during the build out.
BTW, I finally had the van windows tinted: WHAT A DIFFERENCE!!! I put a light ceramic tint on the HUGE front window, which helps keep the heat down and a medium tint on the side windows which makes it far easier to see the GPS when I'm out driving. I hardly need my sunglasses during the day, but I can still see easily at night. It really, really cuts the glare coming through all that glass. I have also added a bug shield, which not only looks cool, but protects that leading edge from love bug damage.
Next? I think it's time to brand this van.
I am trying to decide just how much of a brand. I really don't want it too busy. An understatement is best, so no wrap. I'm thing just a large logo that will fit on the sliding door (and the opposite side). This way it will be displayed even with the side door open. Thoughts?