Fireaxman,
I work in open heart surgery for my day job, though post operative recovery is not my specialty. Congrats on your successful surgery and excellent recovery so far. Phil's advice is generally good... listen to your body and trust your instincts, but don't quit taking any medication without consulting your doctor.
I would suggest that you discuss in detail the kind of work that you do with your surgeon. Handling a chain say, climbing, lifting pieces of wood, stuffing a chipper, etc. are all activities that use a significant amount of upper body strength and apply loads in a lot of different ways.
Obviously, if any activity causes you pain, back off and obey the restrictions your surgeon places on you. Your sternum (breast bone) is indeed held together with stainless steel wires and stressing them before your sternum heals can cause them to break or pull through the bone leading to a much longer healing time, increasing your risk of infection and even possibly permanently weakening your sternum.
For the first 6-8 weeks, you will probably also find that you are less energetic, more easily tired and a bit less mentally sharp. All of this is independent of any pain medication. For some people these effects are hardly noticeable, for some they are significant. Pain medication, beta blockers and other medications all have side effects. For some people, they are minor but for some they are significant. Be aware of the side effects, give yourself time to get used to them and if you find them to be intolerable, talk to your surgeon or cardiologist about adjusting or changing them.
As already suggested, I would also look into physical therapy and make sure the physical therapist know the kind of activities you participate in (again, be detailed and thorough). The physical therapist will provide therapy tailored to your activity and can give you advice on how to avoid injury while working.
Last but not least, don't be afraid to ask for a second opinion, another doctor or another physical therapist if you are not happy with their treatment. It is not too much to expect for them to take a few minutes to listen to and understand your unique job activities, concerns, etc. and to take them into account and explain why they are prescribing a particular drug, treatment or therapy.
Speedy recovery!
Adam