For mouse-only players, I'd guess it's about minimizing precise movement and number of clicks. Since you plan on tweaking the gameplay as well, it's hard to give suggestions. Right now the issue is that you have to constantly alter between two clicks at different positions to make what's effectively only a timing decision. E.g. with current gameplay and balance it'd be optimal to have a default unit and just clicking the customers to equip/send them with the current default - and then for the rarer non-default send, either have a button to configure a specific type for that unit (with that button being a single click for both "select equipment type" and "send them with it") or having small radio-like buttons over every customer visual at all times.
But with different incentives and balancing and features that'll change. The fact that you ideally want one click with minimal "precise"/strained movement for every single player decision never changes though