Structural Engineer Search

As for structural engineers, I can ask a couple of people, I remember talking to a few, without any luck, after we first spoke a few years ago. I have a couple of other engineers that I know now. Just need to find an inventive outside the box thinker...with a structural engineering degree.

Waterproofing really falls into an architect's court. There are some agencies that specialize in "building science" (https://www.buildingscience.com/) and then there are waterproofing consultants (http://d7consulting.com/) that architects occasionally hire -- but typically for very complicated situations. They tend to be on the pricey side, but maybe you can charm some free advice out of them. I also saw you have a handful of architects among your advisors. Any practicing architect should have an idea or two about flashing and waterproofing.

I think your overall plan for a stamped set is good. I do think the liability issue will be a hurdle, but I would imagine some legal CYA language could be added to alleviate this. I will do some asking around to structural engineers though!