You need to have it so that when you buy the power ups (Billionaire and other) you can reactivat them if you turn it off. Have loot picker tell how much is needed to upgrade.
as for the gp it is to make it chalanging so you can't just blow througe the game as for the size if you have a biger tank then it will be slower but it will have more shilding than a little one and as for the bubbles bursting as helth goes down it would seem to me he just thaught it would be to tedious to do that again.