1. About twenty hours over three days and two games.
2. Given I'd never made a physical-game before, I learned I can actually make one :). In addition, I learned that you need to keep the calculations simple when there isn't a computer to do them for the player.
3. Fitting it all on one page. Definitely. I would have liked to pack in more Gobby-lore.
4. Everyone should at least read Grubby Grubby Goblins. Very fun.