1) You can get the latest alpha when you pledge to AppGameKit V2 from here:
http://www.thegamecreators.com/?m=view_product&id=2295&page=pledge
2)No, DBP plugins do not work with AppGameKit it is a totally different animal. AppGameKit is designed to work cross platform so a "dll" for windows would not work on iOS (for example). There is talk of a plugin system in discussion in the forum but nothing concrete yet
3)AGK does allow multiple cameras as far as I am aware but it uses OpenGL rather than DirectX for gfx. Eventually 3D will be much better but currently 3D does not allow rigged models and is very limited. Rigged models and bullet physics are coming but are way behind schedule.
That said AppGameKit V2 is a great tool to play with and for £35 you'd be crazy not to back it IMHO...