1. Yes, the game is complete. The beta is over and the full version of the game is available both at http://www.DesktopDungeons.net
2. Both are for the full version. $15 gets you the game, $25 gets you the game plus the soundtrack DRM-free and the bonus content that was available during the beta.
3. Paypal can accept VISA cards straight without you having to set up an account with them, it's a little confusing, but there should be an option for that right on the first page you see after clicking the pay now button. Alternatively you can pick the game up on Steam with your VISA card with no hassles... Do you use Steam?
4. We're not sure when the iPad version will be released. Definitely only next year.
5. We're not sure if we can do that, but I'm not sure if I'd bet on it... You will definitely be able to play the same savegame between your iOS devices and your PC though.