Hi Peter K,
Welcome to the club that you never wanted to join.
As someone else said, it depends how physical your job is. The official line is that everyone is affected differently but you will suffer the effects of the surgery and chemo is controlled poisoning so that if you are on a 3 week cycle, you will feel quite battered for 3 - 5 days after a chemo session and then you will improve every day until just before your next treatment you might even feel quite good - then back to square one again.
I also felt that the chemo was accumulative as recovery was a little longer each subsequent time. But there are some unknowns about how sick you will feel in the first few days and how bad the drug side effects will be; any sort of steroid will rob you of sleep if taken too late in the day and other drugs mak make you feel somehow slightly removed from reality, but the unknown is how much and for how long.
After mastectomy, your upper arm on that side will have a sort of nettle-rash tingle and you'll probably have no feeling in your armpit. they will show you what arm exercises to do, so make sure you do them every day.
About being self-employed, in this I can sympathise. I am a self employed engineer and spend my day in front of a computer, so it's not exactly strenuous, but I found the mental detachment was hard for me.
I had Chemo on a Thursday, spent Friday & Saturday in bed, moved around a bit on Sunday and went to work on Monday. It was a 45 minute drive so I went early and didn't take my pills until I was safely at work to reduce the side effects. At work I shuffled along like a man of about 90 yrs old (I was 54) and it was tough to concentrate.
I would imagine that if I had a physical job like a plasterer, I would have neede to take on a lad to do the lifting and holding as you really would struggle with carrying and positioning a sheet of plasterboard certainly in the first week of the cycle.
On the other hand I was riding motorbikes in the 2nd and 3rd weeks when I felt like clearing my head a bit.
The only light at the end of the tunnel is that it is usually finished in about 21 weeks - about 4 months.
I hope that helps you to plan things.
Very best wishes
Clunk.