Mine make a pretty nice profit. About 7k per shift
Unless it's a large place, one chef and wait staff is plenty.
I also have nothing on the menu that's less than 4/5 or 5/5 difficulty and my chefs are all able to cook at that level. The recommended dish is always the most expensive two items for adults and most expensive item for a child.
I don't promote anyone but my chef or chefs past 3. My chefs get paid the most and I fire anyone who's unsatisfied at the pay rate of 3. Wait and host staff are easier to fire but food quality is what keeps me at 5 stars. I don't pay for training beyond level 3 for anyone but my chefs.
I also don't train my staff. I hire a townie and manually increase the skills needed to about 6 for wait and host and 10s for my chefs. I promote the chefs to 5 steadily and only to 3 on wait and host. When they're not satisfied I fire them and manually set the skills for a new employee who is happy enough to be a level 2 or 3 pay grade.
The wages were killing me.
I also set to 300% mark up at 5 stars and the sims keep coming and leave 5 star reviews even if it says "consider lowering your cost" I don't.
Those are my tips
Never pay to train just manually set the skills
Fire unhappy wait and hosts at pay 3
Repeat step one after rehire
300% mark up
Staffing only the amount needed
Get all perk points. Use surplus harvest with leftover perk points
Have nothing on the menu (but water) that's below difficulty 4
Recommend the most expensive items when able.