▪Picker view manipulation:  

MG-Picker view adopts very similar rules as you interact with Maya's 3d viewport:

MMB: Pan the view, with/without the alt key.

ALT + RMB: Zoom in/out of the view.

CTRL + ALT + LMB: Box zoom in the view / Reset to its default size.

F Key: Frame on selected picker items, zoom out to show all the picker items if no items are selected.

Space Key: If you are in a multiple-viewport layout, press, and release the space key to maximize and hide other areas, and the space key again to restore. Just like what Maya does to its 3d viewport.

Besides the rules above, extra convenient view manipulation rules are also adopted:

ALT + RMB double-clicking: Reset view to its default size.

MMB Scrolling: Depending on the width/height ratio of the picker content, this will pan the view in a horizontal/vertical direction.
If you hold the ALT key while MMB scrolling, will pan in a different direction other than normal MMB scrolling.

Ctrl + MMB Scrolling: Zoom in/out of the view.

0~9 Key: Frame & Pan the view to show the picker panel with the panel index number the same as the hotkey.
You can use the ~ key to replace the 0 key.

Multiple picker view:  

Usually, a picker tab stands for an Asset or a character. To View multiple characters at the same time:

LMB clicks on the layout switch button at the top right corner of the picker view and selects one of the predefined viewport layouts.
Using a layout other than "Single", more picker views could be displayed in the UI, and you can LMB drag tabs and drop them to the new layout area, or just double clicking on the new layout area, to open a picker file in that area.