I had rotator cuff repair on my dominant shoulder a year and a half ago. I guess my surgeon wasn't quite as strict. I was forbidden from taking off the sling for the first 24 hours. After that, I could take the sling off to take a shower; I just had to leave my arm by my side and not move it. I also had to cover my incisions with waterproof bandages. What was forbidden was active movement of the shoulder. I also wasn't doing any passive motion exercises of the shoulder. I mostly wore t-shirts that were one to two sizes too big; I could easily put the t-shirt on my dominant arm first and then get the rest of myself into the t-shirt. For day of surgery, a truly oversized t-shirt is useful; he can just put his left arm into it and then stick it over his head with the sling under the t-shirt. The ice chiller definitely made recovery easier. I was fine sleeping on my back, but I did use a pillow on my dominant side to help keep the sling level.
As far as typing goes, I was relatively proficient one-handed typing due to a previous injury. Depending upon how much typing he needs to do, voice transcription software might be easier. He'll also have to learn to use the mouse with his non-dominant hand. The only other issue that I had after surgery was shoes. I couldn't tie them while my arm was in the sling, so I wore either slip-ons, flip flops, or velcro closure shoes. Even after I got out of the sling, it took another month or two of physical therapy before I tie my shoes without pain.
The video that annagybe linked provides good advice.
