Yes. You can create whatever you want. A world which is endless, challenges, adventure mode,... all in the same game. The sky is your limit (or not).
To randomize scenes just make them all the same length and BB will take care of the rest or duplicate them if you have scenes that you've made before but again make them the same length. See image below.
But remember, you cannot keep different characters in the worlds, you cannot have different character game play setting in all levels. Let me make it simple, Same characters, same settings for all worlds. Correct me if i am wrong.
This is correct, change in character settings translate to all worlds, regardless of those world's settings.