What about backing/padding/insulation?

If you don't plan on washing the potholder, then you don't need to pre-wash the fabric. If you do plan on washing the potholder, then you should wash, dry, and...

Look on the pump shaft, you usually can see the mark where the set screw was previously. Use the same mark.

Try using GitHub.

No, you have to have a button backing if you're going to secure the button firmly. You're going to run out of room in the button to run thread through...