All depends on what your goals are and what market fits your game-plan/criteria 

Whether the lender decides to do anything, and exactly what they decide to do depends on the lenders particular strategy, target ROI, risk tolerance, current interest rates, interest rate of subject mortgage loan, etc. 

I only buy in vacation markets that depend on tourism to keep their area going.

If everything in the neighborhood is 90 DOM (market dependent)..

It depends on the type of lender, the broker is using.If a broker is using a wholesale lender, they make their money on the back end side.

Depending on the state, when someone rents for a certain amount of time, usually 30 days or more, they become long term tenants in the eyes of the law, and they acquire "tenant's rights". 

This may depend on your market, of course, but in general, if all of the nearby MTRs have it, you are going to want it for your units, as well.

There's many other options in real estate such as syndication and note investing depending on your level of involvement. 

Great idea(s) depending on your market. 

It depends on a lot of factors; primarily the local jurisdiction rules that may limit lease changes (in Portland/Oregon rent, security deposit, screening fees, an no-cause evictions are heavily regulated).