1) If you've been married 10 years you will have plenty of proof of genuine relationship. Proof of joint property ownership, joint bank/credit accounts and the like are good. Send some photos though, perhaps wedding photos, or family photos? You don't need tons, just of some important events. You can also send things like cards, notes, proof of gifts, or trips you took together.
2) Correct.
3) Sponsors of spouses and/or dependant children are not required to have a certain income. You simply need to show that you have a plan to support yourselves (proof you're looking for jobs, or that you have some savings, or that you have friends or family who you can stay with when you first get to Canada). Spouses cannot be denied for medical reasons. (This wouldn't be very humane, would it? Denying spouses to live together because one of them has a bad illness? The Canadian government isn't THAT bad

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4)I'm pretty sure a work permit would not interfere with the PR application, but I'm not sure on that. Perhaps someone else can weigh in?