A patient can 'feel' their limitations and everyone is different after surgery. It is normal for a physiotherapist to assess a patient before they can be discharged here in the uk. I had to walk up 2 flights of stairs and then have a conversation without losing my breath as one test. Another was to be able to clutch a pillow into my chest and give a good cough. As a rule of thumb, patients are told to lift nothing heavier than a kettle for 3 months. This would also apply to small pans etc. I could feel my limitations, if I felt too much discomfort, then I stopped. Getting up from a chair was easy, getting out of bed was more of a task. I did feel very lethargic after arriving back home, tired all the time and a bit nauseous from the pain killer medication. I can honestly say, if I lived alone I don't know if I would have coped.
With regards to arms above head, I was told not for 6 weeks, as this is how long the sternum takes to heal. I wouldn't have been able to turn the steering wheel in a car, let alone have a safety belt pulling on my chest. There are leaflets on such topics in all the hospitals I've been in, perhaps you could locate one.