the answer is basically yes to everything.
The rhythm consists of 20 patterns; 4 variations, 4 intros, 4 endings, and 8 fills. The fills are all independent for each variation; just listen to the presets. Each of these patterns is fully programmable by playing or editing.
A pattern can be intro, ending, fill, variation etc. A variation has 2 independent fills associated with it. Thus pattern in that screen is the rhythm block for Variation 1 to 4 immediately above in the screen. Highlight pattern, press OK, then select a track and you will hear.
Many styles have different intros or endings depending on whether a major or minor chord is played where it makes musical sense. You can make or edit your own as long as you follow the convention of playing/programming the minor intro/ending in Cm (or a minor key with key setting) and likewise the major intro/ending the same as all the other patterns in a major playing/programming key.
The different intros and endings will be triggered by playing major or minor chords, and will follow the harmony of the played chord as normal.
Yep, that's the whole point of the composer, play all your tracks in from scratch in C major (or another key with key setting), and all the rhythms will follow the auto accompaniment just like a preset