1.Packs will work without the pack.png, they just show up as the unknown_pack.png. (if there isn't one in the pack it looks like a grayscale version of the default's pack.png)
2.When you zip a pack highlight the contents of the pack not the pack itself. In other words highlight the achievement, armor,...particles.png and then right click, send to compressed (zipped) folder. Don't right click on Cartoon Simply 512x and send to zipped. This makes the zip have an incorrect file structure which makes it unreadable.
Other than that the pack runs fine as long as your computer is strong enough to run 512x packs.