It is possible to create an editor like the one in the video, but PicaVoxel does not have this functionality out of the box, as it would be different for every game. I've gone into detail on this in the below thread if you want to read more, and it will require intermediate-level C#/Unity chops to accomplish:
The second question is more of a general gamedev/Unity question as opposed to anything specific with PicaVoxel. PicaVoxel creates standard Unity gameobjects with meshes attached to them, so it's completely up to you to how you want to set up your character models. To have a character hold something, you would probably just have a gameobject for the item which would be attached to the player character with a certain offset.
You might find the following thread useful as well, someone created a skinning system that Qubicle and Blender with PicaVoxel: http://forum.picavoxel.com/chat/rigit-workflow-picavoxel-extension