I'll try to answer some of your questions. Our office has a total of about 70 employees. We put the profit sharing and 401(k) into one pot, so it doesn't look like separate plans to employees.
Since we put the plan in place when I was in managment, I hired for myself a new secretary who was an older woman. I value her experience. Didn't even think about the issue that she will work into a higher profit sharing contribution quicker because she was older. Didn't think about health insurance. Would be highly inappropriate in any event. Instead, I worried about the ability to pay her enough to come.
In any event, we designed the plan to put as much pretax dollars away for owners as possible. As a result, every employee gets a decent profit sharing contribution. But those costs are less than the tax savings to owners.