Hi there are a few things I think would be really useful, simple QoL additions.

1. A tooltip on any item that displays current stock of that item across all your own retainers and inventory. This might work like, hold down left shift while hovered over an item and the tooltip switches or extends its window to show this, so that it's not always there (so as not to clutter when unneeded by the player.)

2. A quicker way to move items between retainers, I could see this achieved by either a sub menu on the right click of an item, eg. Entrust to Retainer #2 / Entrust to Retainer #3
OR

3. Add an option to summon all retainers at once, not every command would be available here such as venture explorations, or even selling, but there would be an option to 'Entrust withdraw items' Opening all retainer inventories at once and allowing moving items between them