For #1, I understand you have 60 days after TN expiry or I-94 expiry, which ever is sooner.
Typically your I-94 expires the same day as your TN expires, so you must return by this date.
For #2, that one is more difficult to answer. I understand when you return to US after TN for several years you need to show that you intend to be a tourist (not work) in US and return to Canada within 6 months (to obtain B2 status). To show ties to Canada, to show that you will return to Canada, you should have:
property ownership in Canada (or rental lease)
have a Canadian provincial drivers license
have Canadian provincial health insurance card
have your vehicle registered in a Canadian province, with Canadian Car insurance
have Canadian bank accounts, credit cards, life insurance, etc
file taxes in Canada (show evidence of filing taxes in Canada)
memberships in Canadian organizations would help
I suspect that would take at least 3 months to obtain. (at least Canadian health insurance has a 3 month waiting period)
The longer you stay in Canada the better.
But since you have property in US, I suspect you want to return by Nov/Dec, when the weather in Canada starts getting cold ;-)
Let's see what others have to say. Maybe check with some Canadian snowbird organizations ....