Design Principle of pickers:

There are no rules for designing a picker, you are free to use your imagination to create your pickers.

Yet if you keep in mind these tips when you design your picker, the picker will be more decent and animator friendly.

One picker for one asset, which could be a character, props, or set. Also, organize the picker content with picker panels, say one panel for facial, one for the body, one for deformers, etc.

Keep the picker panel small size. Too large of a picker panel will occupy more workspace for animators.

They could zoom out the view for sure, but the UI won't display as well as the default size.

Tweak the color well, so that all the button colors are decent and not too visually distracting.

Select buttons and use "CTRL + U" to use the button color adjuster to tweak the colors.

Do not use any non-ASCII characters for button labels, command codes, or picker names.

Actually, never use any non-ASCII characters in your picker, such as your own language other than English.

The reason for this is that in the future the picker may be stored in a Maya scene say .ma file, and these .ma files may contain non-English characters,

which will cause the scene to read the issue in an environment that doesn't support that language.

Buttons and their layouts are better if they look like the original controls, it is easier for the animator to identify them.

But do not overdo that, because you still want to keep the buttons simple, and easy to frame-selected by mouse.

One select-button for one Maya control, and utilizes the parent link and the select all command button to help select the multiple controls.

The initial namespace is better to be set to the string that the animator will probably use so that they don't need to set the namespace.

But of course, if the picker is embedded in the asset and if the asset has been referenced, the referenced namespace will be used instead.

Fully utilize the mirror relationship. The animator could mirror the selection using the ALT + LMB, and move slider handles reflectively holding ALT + LMB.

The density of buttons within a panel is better not too high. That will make it more difficult to be picked or frame selected by the mouse.

Use the attribute button for non-transformable Maya attributes, while using the slider for transformable Maya attributes.

If your picker is graphic shape heavy, use one SVG file made from Inkscape or Adobe Illustrator and import them as multiple picker buttons, it has overall better run-time performance than the complex shapes drawn in bezier or polygon.