To awnser you questions: 1. Yes it is intended without a cooldown to "spam" Space to hyperspeed, because you should be able to rise up with maximum of 4 coins.
2. No I can t make it hold because then it would just be "swim faster" instead of Push the character. the Logic behind it is a physical Impact on the character in the movedirection by input of the Person on the keyboard. So thats not possible and would have a total different effekt if it is like that.
OVER ALL - I am happy you had fun with my game !