First, one important advice: Some CBSA officers take the part of their training where they should remain vigilant a little bit too close to their heart. I once forgot to declare a $4 souvenir glass from the Hard Rock Café in New York on my customs formon my way back to Toronto (Mind that they didn't have to find it in my bad, I actually corrected myself within 10 seconds) and the officer said "you can read, right? you have a university degree right? So why did you not read the rules?" and then threatened me that "the next time we could take your visa away". In fact, they can't. (because the Immigration legislation and the customs legislation are two completely separate things). So it's intimidation tactics. While Canada is not the US, "even in Canada" it's unfortunately also the case that depending on your country of origin/your ethnicity, border officers are much more vigilant to some people than to others. At least that is my impression.
What I am trying to say is: Don't think too much about this one incident that your wife had. I know this can be very disconcerning. It takes a while to shake it off, but in the end it was nothing but words.
Now to your actual questions:
1 - You have legal rights as a permanent resident that are thankfully not at the whim of the temper of an immigration officer. If you happen to have bad luck and get to one of the aggressive ones (which are still, IMHO, the clear minority of border officers), remain calm, do not react to their aggression and simply answer all questions truthfully. As long as you are above the 730, you did nothing wrong. Even in the case that you get reported you did nothing wrong. Until the hearing is happening, your life can go on as normal and at the hearing you provide the same proof. But again, don't think too much about the hearing yet, you shouldn't get reported in the first place. If it comes to a hearing they will then decide that you, in fact, fulfilled the residency obligation and therefore you are alright. This will not affect your citizenship application later on at all. Most importantly: No border officer has the power to take your PR status away on the spot. Also, a "report" is not something that in itself is bad on your file in the long run. Just like your neighbour reporting you to the police because he thinks you build
2 - generally speaking, the shorter you have been out of Canada the less "suspicious" you are. That does not mean that cutting it close to 730 is not a problem in that case. There is no "golden rule" to escape more probing questions by the border officer. Generally, the further away you are from the 730 threshold, the better. Generally, the shorter you've been out of Canada, the better. Generally, the more documentation you have, the better. But there is no strict rule as to when they will ask you questions.
In total, though, I would recommend not to overthink this too much. The vast majority of PRs crosses Canadian borders without any fuss. This forum might give you a different impression. But keep in mind that no one goes to an immigration forum and says "Today I crossed the border and nothing happened".