I am amazed that your husband was not referred to an oncologist on diagnosis with metastasising cancer.
As Lynn says, depending on the chemo, and your husband's general health, and, to some extent, luck, he may find it easy or very tough. And as the doctor said, the best outcome would be buying a little time, and that benefit isn't guaranteed.
If it were me - as it likely will be one day - I'd agree to one course if I was feeling strong and positive; and see how it goes. But if I didn't feel pretty positive, I wouldn't put myself through a few weeks of possibly awful side effects for the mere possibility of extending my 'life' by a few weeks. And if the one course was OK, I'd consider the second. I'd refuse to get on the roller coaster of 'I've started so I'll finish'.
What I definitely will do, when my turn comes, is get my GP to refer me to the local hospice. They do outreach (almost all do now), and their job is symptom control. They can advise on pain and anything else that's an issue, and are pretty expert in other local services. And anyone with a stage IV cancer would be eligible.
We get fixated on time, but it's quality of life that counts. There comes a time, for everybody, when the priority needs to be enjoying the life you have, not making yourself miserable by trying to get a little more. I'm not saying that your husband has reached that point: that's for him to decide, and he'll know, not by the number of metastases, but by how they are affecting his life.
But whatever you decide, good luck - and it'll worth hearing what an oncologist thinks.