▪Design Principle of pickers:

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

Yet if you keep in minds 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 body, one for deformers, etc.

Keep the picker panel small size. Too large of picker panel will occupy more workspace of animator.

They could zoom out the view for sure, but the ui won't display as good 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 button color adjuster to tweak the colors.

Do not use any non-ascii characters for button labels, commands codes, 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 future the picker may be stored in maya scene say .ma file, and these .ma file may contain non-English characters,

these will cause the scene reading issue on environment that doesn't support that language.

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

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

One select-button for one maya control, utilize the parent link and the select all command button to help selecting the multiple controls.

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

But of course if the picker is embed in the asset, when the asset been referenced, the reference namespace will be used instead.

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

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

Use attribute button for non-movable maya attributes, while use slider for movable maya attributes.