Carl Sagan wrote:If you wish to make an apple pie from scratch, you must first invent the universe.
1) One of the reasons for Power Level is to have a baseline for the characters and setting so that the PCs are not too weak or too powerful for the challenges of the setting. There are limited circumstances when a PC may go over PL, but they don't happen often and are rarely by more than a rank or 2. Strike 30 in a PL10 setting is ridiculously overpowered. In theory, you would have to give the PC a huge tradeoff, resulting in a -10 total attack bonus to balance it again the high effect. In practice, this PC would have trouble hitting anything that wasn't an inanimate object, but would annihilate anything it did hit. This PC would be difficult to play and even more difficult for a GM to challenge in a PL10 setting, and while the game is relatively open-ended a PC like this would go against every piece of advice about tradeoffs in the book. In short, this PC would break the game.
2) The official Superman build in the DCA book has a Power Loss Complication if he can't interact with the energy of a yellow sun. If that occurs, he loses his powers, most of his STR and STA, and gets a Hero Point. Since he can't fly to the sun without his powers, he'd have to find another means to get there, which could be an interesting challenge for him and the player.
3) Half the series PL rounded down or GM decision. That's directly from the Luck Advantage description. You might want to read what the book says first for some of your questions.