Axial Flux Toolchanger - Mechanism Overview and Tool Plate Assembly Instructions 

Nope there is can be more, only limit is space in the printer

Can have as many as will fit. But need to design some more docks to mount to extrusions at different angles. I am planning add a vertical bar in the front centre hanging down from the top frame to mount two centre docks. Another option is to design docks that mount to the horizontal bar at the back and install the X-carraige backwards. I did that first, but I wasn't having fun working on docks and tools at the back of the printer.