1. Yes 2. Yes (and that would be a good solution to your problem) 3. That depends on where you live. In the U.S., digital costs the same as retail most of the time, though it's sometimes a few dollars cheaper (like with Brain Age: Concentration Training). You also don't have to pay tax on digital games, so that should save you a few more dollars as well. If you live in Europe, though... don't even think about downloading.
4. Zero. And even if something does happen, you can just redownload the game.