Does the tape have to be electrical black tape, or can it be regular duct tape?

This might be a bit of an unorthodox answer, but from my experience, acidity works best for tough spots on brass and other similar materials. Things like lemon juice and...

No. You'll end up with a gross gray colored wig. You might have some success if you dye it over and over again, but your best bet is to just...

You could use regular tape, but it won't work as well as florist's tape. Florist's tape is easier to work with and fits in better with the flower because it's...

No. You need to have double-sided tape to make the tape. If you don't have double-sided tape, you can buy it from craft stores, or any other kinds of stores.

Yes, you can. You can make it into decorative stickers since Washi tape is a decorative tape.

Black is best just because it reduces glare and ambient light, but as long as your tape isn't clear or translucent, it will suffice.

The rust-colored powder, I just wipe off. Throw black spotted ones away. If there is mold anywhere inside the shell throw the whole nut away.