B&B basics
      Since pizza Bob mentioned that his brother was looking for a place to retire in SEA, I've been thinking that I might find two or three more like him as long term tenants in B&B. This was a coincidence - possibly meaningful - and I tend to follow potential Jungian synchronicities. And it also seems it would be easier to have long-term tenants (expats) rather than short-stay tourists. But it could also be a combination of short- and long-term tenants. And for long-stay there should be a room with basic kitchenette - and Vietnamese recipe suggestions and supplies.

      Motorbikes are an essential part of Vietnamese culture. You may not have noticed, but every hotel and cafe and business of any size has motorbike parking - and a motorbike valet, which is essential for the novice tourist. You may want to discuss this with Cynthia. It may be different in Hanoi, but if she's like these Da Nang Vietnamese, she knows how to handle and tend to a motorbike. We could even think of renting them out (via an existing service (as I would do with Tam if this was in Da Nang (because she and son Bao would be responsible for fix-ups))).
What I envision now is.... motorbike lessons. Part of the learning centre - for Westerners.
I will remind you of Anthony Bourdain's great little promo of motorbike culture in Vietnam... "One of the greatest joys in life". This something else that could be offered along with rentals - and "advertised" somehow, like in the description of the property on booking sites. Maybe I could include Bourdain's video. And I've made my own videos of how these Vietnamese can handle a motorbike so elegantly when extracting one from the tight way they stack them. And the driving style. This is important stuff to know - and may be a selling point. You could discuss with Cynthia.
And beyond that - motorbike tours - also provided by existing sevices (as I would use Tam and Lam). [I think this is the way they do things here. They may advertise that they do something, but what they mean is they know somebody who does - and pass the tourist from biz to biz.]

Basic business proposal
It seems to me now that tha ideal situation for a B&B would be to have rooms already rented to long term tenants - like pizza Bob's brother. So now I'm thinking of ways to attract old retired Westerners. But also thinking of "investors"
For example, Eckard and Ron - and pizza Bob also. These are people who are not yet retired, but close. And they have invested in various things successfully.
Eckard - For all the decades I have known him, he has has been an investor - in art, exotic automobiles, and taxi cabs. And he is still a night shift taxi driver. And.... he's a hustler. He has some of his art hanging in various places around town. Private clubs, where everybody knows him. And they talk about potential "deals & schemes". So he's street smart in that sort of way.
So Eckard knows a lot of people in this town - including the high rollers - who may be interested in retirement in SEA - or an investment.
    Fresh thought... 4 unit property for $1500 - rent out 3 for $500 each
      6 unit property for $1500 - rent out 5 for $300 each
      8 unit property for $1500 - rent out 7 for $215 each
      4 unit property for $900 - rent out 3 for $300 each
      5 unit property for $800 - rent out 4 for $200 each