An editor extension to develop 2.5D Games in Unity
Full 3d Physics Support. Use Unity's built-in 3d physics to improve your isometric game .
The toolkit comes with a character controller for your Avatars.
Optimized sorting with minimal impact on garbage collection and overall performance.
Use the Level Generator to create new worlds.
Drag & Drop support. Compose your levels using custom handles for sprites in the scene view. No need to fiddle around with the position value in the inspector window.
Set the bounds of an 2.5D Object easier with visual feedback in the scene view
Make use of the A* pathfinding algorithm that comes with various heuristics.
Extensive Documentation with a Unity like Scripting API
Yes you can use custom sprites that are not part of the toolkit, however you may need to tile them depending on the sorting strategy you use.
This depends on too many factors to give a definitive answer (target platform,other scripts, etc.), but I have successfully tested about 1000 objects sorted per frame on mobile on a mid-tier device.
Unfortunately this is not possible with the toolkit right now. You can only use 2D Sprites.