Have not figured out all of yours query, but want to correct big error about button HIT.
The classic Flash button has four states: UP OVER DOWN HIT.
The HIT just represents the clickable area for the button. You can create a "hidden button" by eliminating any visuals of the first 3 states (UP OVER DOWN) and just define the clickable area in the HIT state.
You can create buttons from Movie Clips, but would still have representation of the 4 above states.
Movie Clip symbols do have their own independent timelines, which can occupy one frame and will run to the end of its timeline (unless stopped). A Graphics symbol's timeline is dependent upon the root movie it is placed in; if the parent timeline is shorter than the Graphic symbol's, it will be truncated. So wonder if using a 'Graphics symbol (or just a plain static image) would solve some of your questions.
See also http://help.adobe.com/en_US/FlashPla...ay/Sprite.html
The Sprite class is a basic display list building block: a display list node that can display graphics and can also contain children.
A Sprite object is similar to a movie clip, but does not have a timeline. Sprite is an appropriate base class for objects that do not require timelines. For example, Sprite would be a logical base class for user interface (UI) components that typically do not use the timeline.
The Sprite class is new in ActionScript 3.0. It provides an alternative to the functionality of the MovieClip class, which retains all the functionality of previous ActionScript releases to provide backward compatibility.