I would avoid using the cordless drill. That stuff is thick and puts a lot of strain on a drill. Cordless, especially only 12 volts, might not have the power to mix. You would hate to have it all go bad while you tried to find an adequate drill.
It goes on pretty easily, but can be messy. Have some crappy clothes and shoes to wear. From experience, I suggest long pants. It can be painful to peel off hairy legs...
Good luck and remember that it is normal to have some bubbles as it dries. It looked awful bad for a day or 2 after I fixed a section of my roof, but it dried fine.
