Hey Gary, I have the shells from Mike boxed up somewhere and could measure the thickness of those, but honestly my idea on re-creating this was to do a somewhat idealized buck and build where a thicker and more durable plastic were used. Of course you can make yours however you want. So just take this for whatever it's worth.
I think the originals were probably HIPS or just normal styrene but decently thick (but a bit thinner than what I sent you for Steve Pielock's microscopes, whatever that was)--works great on screen, but I was thinking an extra-durable replica would be cool where one could take it around to conventions and where we could maybe make a heavy ratcheting door like the first one had, deploying the door without much flexing of the plastic body due to the forces involved. PETG might work for that, but I have little direct experience in vacuum forming and know that some materials are really hard to form.
I plan to do drawings for the plant-ons but just haven't had time yet. @Eric_Ardros or @subxinu have both done this before for their styrene scratch builds and may have some drawings or insights to share, if they're willing.
I think the extra boxes that @hms shows in the photo above are for the pockets that go inside the door.
I think the tricorder slot is cut in by hand, backed with styrene, puttied, and then foam added. It should theoretically be made to fit any medical tric from Mark VI to Mark X. I think the compressability of the foam is what allows for this.
I believe that @Cmdr.Kerner can point you to a font that he made that contains the caduceus symbol. Once I get my vinyl cutter unpacked and running again, I would be happy to cut some for you, but that'll be a few months.