No problem. Keyboard shortcuts ... I know how to change them using System Preferences as long as they have corresponding menu options. It really never matters what they are, I usually re-write the ones I need to suite my tastes anyway.
Just allow that a click on the Content or Format button will either open or close the panel depending on its current state, not just be "stuck" as an open-only button. Then, I can quickly toggle the panel open, review a note that I have made, and toggle it closed. Think ahead especially when that panel will contain other content that folks might want to see then close out. Click(open) - review my note about this paragraph - click (close) - go back to editing.
The question of how the panel expands is a design that I defer to your best judgement.
Thanks for the dialog on this!