If you screw the bolts too far into the motor, it may stop working. This won’t be an issue later, but if it causes problems now, place a few nuts on the bolt before using it. This will stop the bolt from going too deep into the motor.
Make sure the components are well held in place before soldering. Some soldering station offers clippers that can hold the DIP switch and the PCB; however, you can use a ductype to achieve the same.
While using cardboard to protect the table from solder may look dangerous, solder cools very fast, and the temperature of the soldering gun is much too low to quickly start a fire. It would take deliberate actions to actually cause safety issues with it.
Be careful not to cut the cable too short, as it is a headache to resolder a new one to the battery holder.
You need a very short exposed wire to solder to the DIP switch. Try not to strip too much ot it, as it may come in contact with the other end of the switch, effectively bypassing it.
Do not solder anything to the speed controller.
Don’t worry about which electrical contact you connect to the positive or negative output terminals of the speed controller. The cables can always be swapped later.
We used dental floss to draw lines from the clock face diagonals, and drilled the holes where those lines met.
You need not place the clock's arrow hole in the center. As this is a design choice, you can be creative and place it wherever you wish. You can even customise the shape of the clock face as well, so it is not a plain square like ours.
You need not confine yourself to the use of drawing tools. You can easily choose an image from the internet, print it out, and stick it to the clock surface. Or maybe you have other ideas of how to customise the clock face?
Attaching the PCB to the clock face is best done with two sets of hands.