Alt+ Right mouse for selling sounds like a good idea. The stash and merchant interface are closely related, so you’ll want distinct commands for important actions.
What do you mean by numeric perk cost? The cost of using the perk?
Keeping the supply list viewable or adding it to the party UI is also important when you get into situations where you are low on gold and/or food. You’d need to compare the wages of the different mercenaries and whether they have traits that affect their food intake, in order to make accurate decisions when you need to dismiss someone. It also plays a factor in choosing whether or not to give someone a ranged weapon, since you’d need to be able to see how much ammo you have in stock to decide on whether it’s a good decision.
‘Stand down’ I could see as being difficult to implement, because characters take turns separately. So unlike X-COM, where you can undo the stand down order, here you’d be in trouble if you choose to you use it and then wanted to undo it, or accidentally selected it.