However, playing along I'll say the building with less units is either going to be in a better neighborhood or the units are much larger.

We have never built a house and our development research says you can built for all sorts of $$ / sqft and we don't have a good contractor that we can trust. 

I am surprised they are running out of hot water fast, the smaller tanks should heat the water faster than the larger 50 gallon tanks, maybe look into small tank heaters with more heating coils to heat the water even faster. take a look at this one, available from HD too https://www.rheem.com/product/marathon-30-gallon-e...that one may deliver enough hot water for your tenants.

Her unit was larger than mine, and we had equal shares of the common space, but because she came in with a bigger down payment, she paid less of the mortgage. 

If you buy a property, make it have a positive income stream you can probably sell it relatively fast and move your investable cash into a larger complex later.

The only other thing I can think of is trying to start with larger multifamily for buy and holds.Thanks,Dave

In addition, explain that it works sort like a passive income because the money are coming in monthly without her or her daughter lifting a finger!

Any larger multi family I’ve looked into, however, the returns are so much slimmer than they are on the smaller ones.

However,   I know the second company has replaced more flat roofs in my neighborhood and is a larger company.   

The first tenant was able to receive a larger voucher once she moved.