I could propose to them I rent the downstairs room for $800, and the couple pay $800 each, $1600 combined.

Hope we can all connect and combine our knowledge.

from living in the basement while renting out the upstairs just to “save save save”  to combining property with my next door neighbor in order to build high end townhouses.

I use a combination of a few different applications.

I will bite...if you can go conventional loan, the max dti will cap at 50%...off 140k combined annual income, roughly 2692.30/week or 10,769.23/month...using 10,769.23 monthly, I would guess the sum of all your debts cannot exceed 5300/monthly (and some change)...if you already are at 3100, I would guess you have 1900 available monthly for debt service on your house...the lender will use the lower borrow's middle score.  

But, even in theseor “C” neighborhoods, I’m finding the prices on these properties combined with the property tax are more suitable for people who just want to buy a home and not invest.

We actually do a combination like @Kevin Sobilo stated. 

If your objective is cash flow, I would strongly encourage you to look at markets that not only cash flow well but have a good combination of cash flow and economic/demographic trends.

Does any BP'ers living in these areas, see this info as jiving with their local analysis.  10 Cities In Danger Of A Housing Crash This YearBy Jade Scipioni Published April 08, 2019 With Manhattan real estate reporting its longest losing streak in 30 years, and its worst first quarter since the financial crisis, according to Douglas Elliman, it’s no surprise that many cities around the country are in danger of a housing crash this year.According to a new report released Monday, more than 40 U.S. cities are nipping at the heels of a potential housing crisis especially in “old” Northeast and Midwest cities.To determine which areas are heading toward a housing crisis, GoBankingRates.com analyzed data on 175 of the largest U.S. cities.Researchers then used key factors, including the percentage of homes with mortgages with negative equity (also known as “underwater”), meaning the home is currently worth less than the total cost of the mortgage, along with city’s mortgage delinquency rate from Zillow’s February 2019 index.Additionally, the personal finance website calculated each area’s homeowner vacancy rate and rental rate using data from the Census Bureau’s 2017 American Community Survey combined with foreclosure rates from RealtyTrac.To make the list, cities had to have rates of negative equity in excess of 8.2 percent, which is the current the U.S. national average rate of homes “underwater.”Here are the top 10 cities in the most danger of a housing crash this year. 1.

Imagine combining this with downpayment assistance.