1. We're planning to implement CocoonJS's accelerated Box2D physics engine in future. Hopefully this will solve performance issues on mobile.
2. Yep - see the Javascript SDK
3. Yep - try the User Media object and Touch object (GPS isn't supported yet, but could be with the Javascript SDK, or we may support it officially in future as well)
4. That should work with the Javascript SDK, providing it works in Javascript
5. Yep, also included in the SDK download is a custom effect template.