There are a
multitude of possible side effects for Chemo. Not everyone's experience is the same. I'm guessing, but since he is good health/shape, the chances of your friend having the more serious side effects are low.
My mom had Breast Cancer. She was lucky in the fact that they found the tumor early and she did not need a mastectomy. Just the tumor and lymph nodes along her left side were removed.
She lost her hair. When it started, she said "Screw it!" and shaved her head. She got a wig from the wig/hair salon that assists the Cancer Treatment Centre she was with.
She lost weight. It was about 15-20lbs.
After the first month of Chemo, she had less energy and would be sick throughout the day.
She kept working for a few weeks after she started Chemo, but then had to stop once her strength/energy depleted. She's a strong, hard-working woman(and stubborn), so for her not to be able to work, that really bothered her.
In our family, we are not a sappy, lovely-dovey bunch. We were there for her for whatever she needed, but also kept the mood light and didn't dwell on her having Cancer/going through Chemo.
Once her Chemo was done, she went every 3months for check-ups for 1yr. She now goes every 6months. That will continue indefinitely.
It has been 5yrs and there has been no sign of the cancer returning.
As for lifting his spirits, that is different for everyone. The main thing I can think of, is to treat him no different then you do now. He's the same person.
A lot of the time, family/friends can treat someone with health issues with "Kid Gloves". If you don't know that expression is means 'To treat something very delicately or carefully.' You know him best as to know whether or not to do that.