It depends on different factors, f.e. if you are working alone or with a partner, if you do it part time or full time, and on the size of the fleet of course. Higher or lower utilization of the bikes has also to be taken into consideration.
From our experience, we know that one person working full-time on the project can maintain up to 200 bikes. For higher number of bikes there are economies of scale so that for 1000 bikes, not more than 4 full-time mechanics should do the job.
We recommend visiting hubs 2 times a week, before the weekend starts and after the weekend for the system usually has the highest traffic from Friday morning to Sunday evening. Therefore, best practice is to make sure bikes are in place and ready to face the weekend and then check them after that.
The goal is to ensure quality of the bikes and happier customers.