I'm a Realtor with a couple properties listed in Boise, ID and a neighboring town for my investor/client that are currently rented as co-living or rent-by-the-room and getting killer income. (7.3% - 9.5% Cap rate) So far, every inquiry has been baffled by the concept of co-living or rent-by-the-room and immediately ask if they're being run as a halfway-house (which they are not).

Hence, this is maybe why your occupancy rate is dropping nowadays. 

Don't forget that a lot of these old gurus started when the interest rates were near 0% and the house was a half price of now with 0 regulations.

And the values like all rentals will just track the rental rates and what an investor is willing to pay for a return.

You'll have depreciation shielding your passive income, so that's a 35% savings on your marginal income. however if you flip you'll be subject to higher tax rate - so you'll have to figure out what strategy works best for you.

(Maybe the seller has a great interest rate, but you would have to pay twice that amount which wouldn't be profitable.)11) Crime in the neighborhood. 12) High turnover in tenants (raising your expenses.)

Who cares about lifetime interest costs, except to the extent you can easily lower them (refinance to a lower interest rate) to increase your cashflow.

Brandon Turner's Rental Property Investing book is an excellent primer to understanding the happy path for purchasing a property - however in this market it really comes down to having bulletproof assumptions on rents/taxes/R&M/etc. as with rates as high as they are/inventory as low as it is, there is less cushion in your returns if you analyze properties with bad assumptions.

Interest rates will not be low.

You have to adjust your expectations to match current reality, which includes higher mortgage rates, higher prices, more expensive taxes and insurance, more competition, etc.