My last post disappeared after my login timed out so here goes a quick reply:
For level transition, do you mean show the last level as moving to the next? A solution might be to take a canvas screenshot of the whole level (keep player over top of the canvas and don't paste them into it) with a global object, then change to next layout and have the player walk in over top of this canvas object, as it scrolls into the layout (unbounded scrolling)
What do you mean music system? Making an audio object global will allow it to play continuously in every layout if you mean to keep the same music playing between layouts.
As for entering the rooms/respawn, are the levels pre-designed and hardcoded, or randomly generated?
If pre-designed, you can just add a new invisible sprite at each doorway with a private variable (eg: EntryID). Then when player dies or at start of layout re-position player to the sprite where EntryID = global variable PlayerSpawnLocation (set this at the end of last level).
Hope that helps!