Firstly see what you can afford currently from a lender.

If I'm saving for the down payment for my next real estate investment, I would put the money in a more liquid type of saving or investment product.

Somalia has over 40 million livestock and almost zero feed pellet production.

All good until today, (2 weeks after signing new lease,)  he calls me and says he miscalculated his expenses, thought he could afford it but now he cant ect ect.

I'm doing this for the first time on my own after a divorce, so I'm aiming for efficiency, affordability, while also being able to find tenants I feel good about being such close neighbors with.thanks in advance! 

What if the roof requires replacement but Partner B can't afford their share?

You should make sure that you can afford the cost of the protection that you choose. 

Renting to your mother would make it an investment property and eligible for a 1031 exchange.There is no statutory requirement for income production to make a property eligible for a 1031 exchange.  

@Edward Heavrin: Both options, but at a high enough equity you kind find long term mortgage products that will allow cross collateralization, so you can use those high equity or free and clear assets in lieu of down payment. 

ROI and financial gain are truly the best catalysts for solving big problems like housing affordability and availability.