I require proof of income, and verify it by contacting the human resources department of their employer in writing. 

Expensive markets are often desirable because many people want to live there, driving up demand and prices.Reno, NV, for instance, is a market that benefits from diversified employment sectors, including tech manufacturing, hospitality, and recreation.

As an investor here myself, I can tell you we're seeing solid rental demand here thanks to the strong job market and major employers developing here. 

Real estate's "gross rent multiplier" is Wall Street's "sales to revenue",  "cap rate" is roughly "P/E ratio".When evaluating markets and investments I tend to start with GRM (or lazily the 1% rule), then attempt to return a cap rate based on assumptions about costs, then I work my way to multiple years of projections (assumptions about inflation, amortization, tax benefits, etc), and if I am partnering with one of my smart friends I have to pull up an IRR (internal rate of return).I also look at regional employment levels, median income to rent ratio in the zip code etc. 

HELOCs are much tricker than a closed end second - they don't typically allow you to close in an LLC and they are full doc qualification, meaning your FICO, employment history, income, DTI etc all come into play.

You typically need up to two years of stable employment before a bank will loan to you.

Solid employment history.  

I use the 3x rent for my first barometer, steady employment, good credit, and of course 3 years of rental history.

I'd definitely recommend considering the Columbus OH market - it's got strong macroeconomics with major employers coming in and developing here, steady population and job growth, and prices that still make sense for cash flow.

I'd have them sign my own lease on renewal and I'd make sure I had enough information on them so I can go after them if a legal issue arises such as employer and other similar data.