What is generally done is to have a mouth corner bone, when it’s moved up it drives a smile_R shape, when moved down it drives a frown_R shape , because you don’t use smile and frown shape at the same time it works.
You can also use the left/right location of the same bone to drive other shapes that extend or contract the lips. That way one bone can control 4 shape keys already.
Both setup are doable, the main issue with controlers parented to the face is that it can get hard to animate when the character is in a strange position. One way to workaround this is to parent a camera to the head , like in the Boon & Pimento rig.
The other solution is to have a dedicated panel. that is cleaner, that also allow to really see the face without any disturbing controllers, but that takes more screen space :
There are no standards for interface but there are good practices that you can find on many professional rigs, try to look for some professional rigging demo-reels for inspiration. If you work with professional animators ask them what they need and design the rig’s functionality with them.
Also don’t be afraid of making mistakes, world isn’t perfect and rigs either, a good animator will always try to work around limitations and will make something good out of it. Of course it’s better for them if they can concentrate on their work rather than put their energy on messing with the rig. Once your project is done try to get feedback from animators and they will point out what to improve on the next project !
Good luck ! and thanks @3dioot for still remembering B&P thread, I hope you’re doing well !