I use DO a lot so my Sims can dine out, but I occasionally run a restaurant as well because I want them to have a 5* restaurant to dine at. From this experience I would say that I would not recommend running a restaurant with more than 10 tables and allow for space between the tables, I'd say at least enough for two Sims to pass through. Also, if it is a restaurant you are planning to run, keep the kitchen and dining area on the same level. Train your staff up as quickly as possible and regularly check their satisfaction level. Raise the salaries as needed. There is a bug with a table not receiving their order once in a while and then leaving after a few hours and giving you a bad rating. It is frustrating when it happens but it does not happen so frequently that your restaurant can't be successful. I usually get my restaurants to 5* level within 2 in game weeks.