Why do I need to add the empty paper towel roll?

You can use rags instead. However, paper towels are not going to leave fibers behind that could later block your gun when it is in use, causing you to strip...

No. When you erase files, you create holes where the file data was previously stored. It's because of these holes that there is a need to sometimes defragment an HDD....

Yes, you could use 4 empty toilet paper rolls. I did mine with tin and rivets.

Yes. It will last far longer then cardboard..

You need to find something much larger than that for a millipede habitat. It is suggested to have a 5-10 gallon container.