GarageBand mainstage for creating a simple bass player for live gigs

I am looking for the possibility to use mainstage to create a simple bass player for live gigs. My idea is to use the arpeggiator to create rhythmic patterns and use the klick and live piano playing via midi to have the right timing and note.

But it seems to be not possible for 3 reasons:

• The arpeggiator does not support just one note repetition e.g. root note so that the bass patterns taken from the keys are always using the whole accord notes, even if I tell it just to use the bass-area of the keyboard it makes an arpeggio from it. Any idea how to change that e.g. analyse the chord and just use the root note
• 2nd issue is more severe: The arpeggiator does not sync to the tempo of the klick. When pressing the piano note in a live setting and it is a little out off time, the arpeggio always stays out off time. What I need is that the arpeggio that is active always plays similar to the klick using the note that is active. What can be doe to ensure that?
• How can I switch between several arpeggios representing different bass patterns per song part? I did not figure out an easy way to do that. Any idea on that?

Thanks in advance

Jan