Paul, stand tall and in writing let your employer know what you can manage and what you need to arrange trades people to do. Your utterances here tell me you believe the expections of your employer are over the top so tell him / them how you see it ! You maybe contracted to the business but you can mentally & physically only do what you can manage safely. Ther must be a written agreement between you revise it and discuss it with the owners. You are set to high speed all day, this cannot last. Do not just talk with the owner about the situation show on paper how unmanageable it is and show a plan you can comfortably support. Perhaps consider opting out of the contract if no reasonable solution is reached.