If I've witnessed it (typically loud music/TV) I don't renew their lease. 

., i would use a Texas Instruments BA-35 Business Calculator which has all of these functions built in for you to amortize a loan and determine PV and FV.

Multifamily living tends to be louder, imo, with more parties and people out making noise/playing music etc.

The MOST important thing you should do is have a lawyer write or review your company operating agreement (if you have not already done so)I think starting out with full featured property management software has been instrumental in allowing us to scale quickly.

When signing, the big documents are the Note and the Deed of Trust/Mortgage (title of the document varies by state, but it is the security instrument that gets recorded at the county).On the Note, check that property address, loan amount, interest rate, lender, and first payment date are correct.

You also never have to get your hands/clothes/car/life/wallet dirty with renovation projects.Right up front, you have the civility and simplicity and predictable(ish) closing timing that comes with buying from a production builder, rather than trying to play musical chairs with other investors and the resale market.

A HELOC is a short-term debt instrument, not one suitable for a long-term buy & hold. 

Or a mix of active and passive so you can fit in your golf, reading, music lessons, travel, and more (manifesting myself here...). 

Maybe a pitch that they are getting their "own house" for the same price as an apt, if that is indeed true ("Tired of thin walls and loud music at 1 am? 

Lately theres been a new legal instrument called a series LLC.