The staff number depends on the size and specialty of the restaurant. If you have a self-service restaurant where the dishes just cooked and not deliver to tables, you can have one server per shift for every 12 tables. It would help if you also had a cooking staff of 4 people for every 50 customers.
If you have seating places for guests and servers for them, you need one server for 4-5 tables and 5-7 cooking stuff. But it also depends on the intensity of gusts coming.
There are also other workers needed for your restaurant; cleaners, cashiers, chefs. The more high level of your restaurant, the more stuff you need to offer better service for your customers.