If you would assign workers to stores individually, you need two workers per store, where I usually have more like 3 workers to 2 store, so I wouldn't want to do that myself.
Not that I have a great alternative; I make my work zones a bit larger including a mixture of 4-6 enclosures and 15-30 customer facilities that are close together around a central staff room (or two, three, whatever), since it's not like the keepers and vendors will get mixed up who's doing what, and it allows me to have fewer zones to manage. I think this works out well for cleaners too, since they only clean near what's in their workzone, and separating things out too much can result in paths between workzones getting neglected. The downside is I end up with a very long list (30-60) of staff and facilities in each work zone, and when it is long enough that you can't see all of the list in one screen keeping track gets really hard.
I cannot overstate how much easier it would make managing larger workzones if workzone lists could sort staff in order based on their job, rather than their first names (which while nice to have, are completely irrelevant to the work zone, I want to know if I have five cleaners, not five Freds), and if it would list "facilities" based on anything at all, like put staff buildings first, then stores, because right now it is completely random. I have at times taken to naming people/buildings based on their category, but renaming hundreds of staff and buildings just so I can count things gets unwieldy, and can't even be done in batches when you are making stores, since they are auto-hired one at a time.
I am quite happy with how larger zones work functionally when I have finished setting it up, but it is SO HARD to make sure I have the right number of vendors per store and mechanics per habitat, toilet, ATM etc, staff rooms per staff and keeper huts per habitat, since the vendors and mechanics are randomly scattered through a list of dozens of people, and the stores, ATMs, toilets, staff rooms, and keeper huts are all randomly listed together in the workzone list of dozens of facilities! I am looking at one list of facilities now, and have no idea how it decided what order to put these, it's not even sorted by what order I added the items to the list, or what order they were built in, I really have no clue. As it is, it's nearly impossible to make any changes to a zone and be confident I have everything in balance.