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I'm not doing quotes around each of your questions, you'll just have to figure it out ;) Also I'm feeling a little snarky today.
- how for husband (in high-earning career) to save face when workplace peers and close friends live in McMansions?
He will do his very best to not mock his colleagues for having giant, pointless homes when he is invited over.
- how to survive with one bathroom if the whole family gets food poisoning?
Assure them that you have a sizable stash of buckets. And bleach. Hey, they asked! If they insist on continuing the conversation, go into "the plan" in *excruciating* detail until they change the subject.
- how to secure excellent stable neighbours if not buying into a really good (read: more expensive) neighbourhood?
You don't want to expose your family to the kinds of values endemic in Those kinds of neighborhoods. Did you know the Stanford rapist came from a "nice" neighborhood like that? In seriousness, there are small homes (even apartments) in perfectly good neighborhoods if you look hard enough.
- how to comfortably house guests, especially the 4-7 (7 if future spouses come) close family members that live far away but we love to have visit?
Use the $$$ you're saving on your mortgage to put them up in a hotel. Or they can sleep on the floor. Or a tent in the yard. Their choice.
- how to give multiple kids their own space?
Put each kid in a storage tote. KIDDING. But as I mentioned on someone's "can our kids share a room" thread, "own space" does NOT have to be "own room." Kids have shared rooms for the entirety of civilization. And that way they get practice for college.
- how to get kids attending excellent public school if not buying into a neighbourhood with bigger nicer homes?
Point them to Palo Alto, CA, which has experienced a rash of teenage depression and suicide, often traced back to the academic pressures they feel in the "excellent public schools." [https://www.mercurynews.com/2017/03/03/cdc-report-youth-suicide-rates-in-county-highest-in-palo-alto-morgan-hill/] But actually see above about nice neighborhoods... I went to great public schools (in the US) while my parents rented 2 BR apartments for 5 of us (for a short 2-year stint, a 3 BR). This will have more strength if you come up with some examples...
- how to store all your stuff and not have to be super minimalist?
Why *not* be somewhat minimalist? A small house will have plenty of space to not have to be *super* minimalist. You aren't looking at "tiny houses" are you? Efficient shelving. Stuff under the bed. If worst really comes to worst, a storage unit for the long-term storage stuff does cost less than twice as much house...
- how to have adult relations with your partner and not have to run down the hall to the bathroom afterwards? (See: living without a master bedroom ensuite).
Buckets. Kidding! But seriously put on a robe and walk, don't run, to the nearest bathroom. Keep some wet wipes by the bed for on-the-spot emergencies. Where's the problem??? I'd be more concerned about noise...
- how to host large dinner parties (and in general be social and have large groups over) during Canadian winter (can’t eat outside) or other poor weather circumstances?
Buffet style instead of sit-down dinner. Rent out a space. Co-host with a McMansion friend (you cook, they clean!) Be an introvert and invite smaller groups. Or just invite smaller groups more frequently. Finally, my parents definitely had upwards of 20 people, seated at a table, in the 2-BR apartment's living room for their moving-away party... they lined up several folding tables with our dining table, close friends brought extra folding chairs. Great fun was had although at one point our Christmas tree was knocked over :O . But it wasn't really a problem.