Tutorials for cs5.5 + starling

Question

I buy some 2d vectors , backgrounds , enemies , heroes and platforms. i make already a game for android with adobe cs5.5 but i have some lag and gravity issues. So, i decide to make it again from the start using starling. The way i draw my game is simple.I like to have my enemies , coins etc to the stage and not dynamically add them. So , is there a good tutorial for me to explain gravity , hit collision with ground and enemies?

Also i would like to know if writing a code in timeline or in classes is better or its not a big deal if the code is good written. Thanks!