The creeper spawn limit is 25 and the total hostile mob spawn limit seems to be 50. I tested this with in survival mode with a spawner that only spawns creepers, zombies, and skeletons. Different mobs may produce different results but I'm sure about the creepers. I don't feel like testing spawning parameters but it does seem to be the same as the wiki says. Hope this helped! This is after TU 14 btw
No, there is not a current method to reset the end and beat the EnderDragon as many times as you want. Unfortunately, you'll just have to create a new world and go through the process again. I believe there is a method to do this on PC, but with the limitations of file editing on consoles, there is no method for resetting the end on your Xbox.
Best Answer
Be careful that it gets affected by gravity, just like gravel or sand.