It would be super convenient to have a button that would let you move all of a characters items to the storage with one click (possibly with a confirmation dialog).
A common suggestion, and I think most players would support you on this. As a poor stand-in, you CAN create a saved build with the Store/Retrieve button where no one has any equipment. Call it "Blank" or something so you remember. But this isn't ideal if you also use lots of different characters, as the active characters are stored at the same time.
I think the character stable should just be handled differently. We already can store parties with their items. I think when you stable a character from the party, his items should return to the item pool/your chest.
Hold control, left click each item slot. It's not *as* fast, but it only takes a few seconds per char.
