Hi, Tappy,
A question - Is the rib/lung pain there at all or random times, or is it worse when you take a breath in or breathe deeply? If it hurts when you breathe in deeply, you may have some fluid build-up in the lungs. This can be from just the irritation of the lungs being deflated and manipulated during surgery. It may resolve by itself within another couple of weeks. If it does not get better, ask your doc. Mine told me to take ibuprofen to help reduce the inflammation, which reduced the fluid production and pain.
As for rehab, my own opinion is that it is highly valuable. Prior to surgery (at age 63) I was a 5 days a week gym rat. I jogged, lifted weights, exercised. . . did all the things guys 10 or 20 years younger were doing, just slower. After surgery (and after resolution of some complications) I did 12 weeks of cardio rehab. The rehab was about an hour a day, 3 days a week. I did the same routine at my own fitness club the other 2 days a week. Within those 12 weeks I went from a weakling couch potato back to about 80% of the conditioning I had a couple of years before surgery. It really helped push me to get healthy again, and it gave me great confidence when they pushed me and I found that my heart wouldn't fail if I worked it hard. You do only get out of it what you put into it, but the value is there for the taking.
Work? I also work a desk job. I thought I was ready to go back to work at about 4 weeks, because I was bored. I started with some remote office work, and it is a good thing I did it that way. For the first week or so, I could only concentrate for a couple of hours, then had to let my mind go for a while. I would not have wanted anyone to see me that way. After week 5, once I was released to drive again, I went back to work part-time. For weeks 6 and 7, I worked about 4 hours a day. Week 8, I went up to 6 hours a day. After week 8, I was back to my "normal" 10 hour work days with trips to the gym after work. There were still days when I couldn't push hard all day, so listen to your body. Don't over-do it. If you over-do things, it will take a longer time to recover than it used to. After all, you are still healing.
And healing. . . well, we all heal at different rates. I would say that I healed to about 80% pretty quickly, maybe within the first 4 or 5 months. It wasn't until about a full year after surgery that I finally realized that I was back to 100% (and better). Take your time. You will get there.