What should I do after defeating all these bosses?
Solution 1:
Use the pwnhammer to break demon alters, this will cause some hardmode ores to spawn on your world, mine them to make better gear, fight some mechanical bosses, (for info on how to summon them see terraria wiki) Kill planterra (again, visit the wiki), Farm the dungeon for ectoplasm and try to fight the waves.
Note: not sure how much of this is relevant to pocket edition, Please edit out anything you're sure isn't.