1. If paypal wasn't safe then I don't think Scirra would use it as a way to purchase things in their store.
2. Yes you can do that. You can name the account anything you prefer and sign up with your dads email. You can also add your email so you can edit while signed into the your own account. Any transactions will be sent to a google merchant account or your dads bank account.
3. No, you will only pay 25 dollars like it says.
4. Depends on your game. I made a game for google play and am selling it for .99 and it has gotten 2 downloads in a 4 month period. I also consider the game to be one of my best.
5. You definitely can get personal experience from this. I would know because I am selling in my father's name too.