Do I have to give my employees health insurance?

Only if you average 50 or more full-time equivalent employees in a year.  That said, if you want your company to provide health insurance for your employees (and most companies do), then you have to provide it for all eligible employees.  You can limit health insurance coverage to only full-time employees, but note that a full-time employee is defined as an employee who works 30 hours or more per week.  In addition, there are some legally entitled leaves of absence that employees can take under California law for which you would need to continue to provide health insurance while they are on leave.