I kinda like the trackpad and function buttons on the 9900 for UI. Are you planning on a touchscreen to navigate the interface? In my experience, touchscreens quickly become a problem in outdoor conditions the hiking and emergency use-cases would likely see.
On the greycat device they renamed the dotted Blackberry icon the “mesh” button, which I think is adorable.
Anyway, I’m just throwing out resrouces that might be of interest and/or speed folks up. To that end, I had overlooked that images, schematics, design files and various hardware info bits are still available this repo: