That account always starts to make me smile JUST before I need a new roof or something along those lines.I have no clue how your 15 units are configured, but I would guess 20-30k on hand in cash would probably be a good idea.

We have never seen a loan configured like that and just didn't understand it.

Just make sure unemployment rates aren't too bad.They also don't seem to like older houses where the rehab can be more complicated or odd configurations like a 2Br 2 ba.Also be sure to check how many properties are offered for rent where your looking.

I do realize though that they will have control of the final configuration of the deal. 

Assume "good" real estate market conditions...My (severely naive) conventional wisdom tells me that if I build a 3/2 home on a vacant lot, my "All In" costs for the home would be considerably less than if I were to purchase a home of the SAME configuration on the same lot.  

It is just an IRA configured differently to invest in things outside the Wall St exchanges.If your mother can get a good cash flowing property or two in the IRA, she should be able to leave the principal in place secured by that real estate and draw her required distributions off the income produced.  

Or weird configuration (e.g., one house behind another)?

We are flexible with configuration.  

Do the rest of the houses have master bed/bath configuration?

It needs to be valued at it's legal use, not the illegal use it may be configured as.