Retirement and Health Care questions

Hi,
I would appreciate it if someone could give us some answers/advise on the following situation. I am a U.S. citizen, 60 years old. I am a diplomat with the U.S. government and my husband and I live abroad. My husband is Canadian. He is 61 years old and is not employed. We married in the U.S. 3 1/2 years ago. He is a permanent resident with no conditions on his residency. Before we met/married he was on disability in Canada for about 2 years. My husband is thinking of becoming a U.S. citizen and I have thought of getting Canadian citizenship also. When I retire at 65 from my current position, we'll probably settle in the U.S. Couple questions:

1. Can my husband collect old age pension from Canada and live in the U.S. when I retire?
2. Can my husband collect spousal social security benefit from my social security? And can he collect both from mine and from Canada?
3. Is it worth it for me to become a citizen of Canada? For example, would I collect his old age pension if he were to die?
4. Would he be eligible for medicare in the U.S.?
5. Would it be smarter for us to move to Canada to retire, financially speaking, that is?

Lots of questions, I know. We're just trying to figure it out if it's worth it for me and him to have dual citizenship?

Thanks,
CanadianSpouse