You might consider using the "Ranch Animal Day" event from Horse Ranch as a way to attract visitors/earn money while playing as the Zoo Keeper. It's basically designed as a way to run a petting zoo:
> You can invite random unknown sims, which for a public venue would make sense. This is a feature of the 2 events that came with HR.
> Guest/Helper Sims will interact/care for animals autonomously, so the animals get some socialisation and some needs met.
> Reward/Prize for hosting event is cash, so it pays for upkeep/improvements.
> You can host them whenever you want, so can take time off from hosting as needed, or add in market days for the produce sales.
> Friends of the resident can also host parties on Residential lots, so you could also host them from "guest" households (who have met and befriended the Zoo Keeper and added them to guest list) and then gift some/all of the prize money to the Zoo Keeper for upkeep.