Character points are redeemed every 25 play point
So if you have 27 play points and redeem 25, you will have 2 play points. And when you earn another 23 play points, you will be able to redeem another 25 character points
Your questions do confuse me a little, and since I don't personally use the play feature often I don't want to mention anything I could be wrong about -
But you can only redeem character points (25) when you've achieved 25 play points.
If you have over 25 play points, say 80, you'd be able to redeem character points three times (75), and would have 5 play points leftover. These would go towards your next redeem, so you'd only need another 20 play points.
Your play level won't decrease when you redeem your play points.