I started my build with similar thoughts. See: "Large Family Sportsmobile" thread.
A couple of things worth considering:
1. The PH bed is a little on the narrow side for two adults. Not that it can't be done. I would just recommend that the two adults that plan on sharing the space try it out at SMB ahead of time to make sure it will work for you. The Sprinter is a little wider than the Ford, don't know if that translates to a wider PH bed or not.
2. The area behind the benches can have some limitations for bed space as well depending on how tall the people are that plan to sleep there. So, depending on how tall you will dictate on if you are able to utilize the space widthwise or lengthwise. Again, the Sprinter is a little wider than the Ford.
3. I've got the Sprinter seats installed in my Ford. Ultimately, they are too big to get around to access the rear platform bed. The point being to make sure you can crawl over/around to get to the bed.
I like the idea of converting the passenger van to "sleeper" with a PH bed and rear platform. A couple of considerations there:
1. If you can, get one long enough so that you can take out both the first and last rows of benches and still have enough seating. Last row is obviously for the bed. First row is to give the "living" space the "50" plan is so famous for. In my opinion, a little elbow room goes a long way and gives you all kinds of options when configuring for specific trips.
2. In the case of the Ford, adding the PH top means losing the a/c vents over the rear seating. Don't underestimate the significance of this. In the heat of the summer (granted in AZ), it can take 30-45 minutes of driving with the a/c at max both front and rear to get the interior temp down to something reasonable. Not cool. Reasonable. I don't know where the rear a/c vents are located in a passenger configured Sprinter.
Hope that helps.