A few immediate thoughts:
» Wow this is epic.
» Instead of Arduino, you'll want to use a ChipKit since those can actually work fast enough to make acceptable graphics. Plus there's a framebuffer library for it.
» You can use resins and molds to easily make the final dashboard. What's great is that you can sand and finish a 3D printed part and that now-perfect finish will become the master part.
» We need something like GitHub, but for code, CAD drawings, and documents. (I hate github, too, it's too hard to set up work flows)
» Once the software and electronics requirements are finalized, we'll figure out the lowest price hardware that can run it. We probably won't need a custom PCB made, since the crucial restraint will be the display.
On the software for the screen:
» If each function were to be made into modules, it could be easy for the user (person riding the bike) to add and remove functions.
And in case you didn't notice... WOW!