Nicely done.
Perhaps the backwards could be cleaned up if you re-calibrate for level.
FYI: Most gimbals are not "secured at the top and dampened underneath" - although thats common for the DJI Phantom gimbals. That method is generally called Suspension dampening.
Gimbals like the popular DYS, and many many others, use Compression dampening, which is generally considered to be a better approach (although the Phantoms are pretty damn smooth so who really knows).
(FYI, I'll throw something at your kickstarter)