Your labor rate should reflect what the pay scale is in your area. As a rough rule of thumb your rates should be at least double of what you pay your journeyman or apprentice.
You have to allow for things likwe work comp, unemployement insurance, SSAN matching, increased cost of business insurance for additiional employees, vacation pay etc.etc.etc.
You have to get all your costs back in your rates or you will not be able to pay your bills. And a profit would be nice.