Platform games advice.

Hey guys I always wanted to make a platform game like Doodle Jump.
so my question is : should I make my game mode endless or separate levels ?
if its endless, how do I make my game repeat ?
if the level is repeated, wouldn't the game be predictable ?
and how to I make the platforms change behaviors when the player reaches a certain altitude ?
Or randomize the platform behaviors when they reaches a certain altitude.
 

For randomize platforms, see this post:
http://community.stencyl.com/index.php/topic,10420.0.html

Is there a tutorial for this ?
I am new to all of this and I would definitely appreciate all the help I could receive.
I need tutorials and guidance