Will the Pi Zero Micro USB ports continue to work after installing Zero Stem?
The existing USB port will work as long as the Zero Stem USB connector is not plugged in to a computer or hub. The power connector will continue to function as normal.
Can the camera connector still be used after installing Zero Stem?
Yes, but it is a bit difficult to plug in the camera cable after installation, so I recommend plugging in the cable first.
What size are the mounting holes?
The mounting holes are M2.5, the same as the Pi Zero. However, M3x6 mounting screws and bolts are supplied in order to prevent any sliding between the Zero Stem and The Pi Zero.