Custom module help requesst

I got confused about the rules of trays vs buttons vs rockers, etc when I tried to create a custom module for an activity. This has to do with trying to create a “House” activity that would have a module with the buttons for my HTD multizone amp all in one place.

I created the activity and added custom module. So far so good.

In the “0 Custom” section I can add a button but not a rocker. What is the rule here as in is there a path to adding rockers in the Custom section?

For the “1 Tray” I can add buttons and rockers, but there is minimal I can do about arranging them. Are there options I am missing?

Is it possible to have a tray auto expanded?

I think this is doable and I am just missing the best path forward.

Thank you!