You could try tin snips. I have found these cut everything (laminate flooring, etc). Link: https://www.homedepot.com/p/Wiss-12-5-in-Straight-Cut-Tin-Snip-A9N/204155040.
Yes it will work perfect for what you want to do.
I think I would choose an item specifically designed to move heavy furniture for your appliances. I think I would only move lighter furniture with these pads on the legs.
Yes, they would work great for that! Great idea!
If you try them, you might want to double them. 400 pounds is a lot to ask of this type of product. It doesn't have a plastic layer like those furniture moving pads.
I assume you want to stack them, one pad on top of the other, to have a thicker result. This might work if you use the whole pad, or a large portion of it, but since they're really designed to stick to smooth surfaces, they may not stay together if you move/slide the furniture they're attached to. Probably not a good solution.
I think you would be able to but if the metal is very sharp it might cut through the felt pad itself.
This pad is 1/4 inch thick! Very thick and sturdy.