Ok first, retail isn't a career it's a business, sims that already have careers can start a business at any time. You can even have a doctor-veterinarian sim if you want, you just have to manage the time for both.
Second, retail is fun you should do it more often.
Third, if you take a household to an NPC store it should be open like any community lot, even if you did rotational, but I think it'll have random NPC employees, but that I'm not sure as I don't play rotational much.
PS: be advised, there's no shopping bag animation. :(
