Since we are stepping into a new horizon we want to make sure we protect ourselves in the best possible manner.

The view is at the horizon of a lot of other stuff.

I don't think you need to worry much about a peak in MF If you are a buy and hold investor with a long investment horizon.  

I definitely think a downturn is on the horizon that will affect various markets differently.

With only 20 years on the retirement horizon, do I go with a 15 year or 30 year mortgage?

You would actually have to determine what is your goal of investing, your investment horizons and liquidity needs.

Once the baloon comes due then move on to the next investment after a 5-7 yr period and take the CF over the short time horizon and 1031 the appreciation.  

Again though, I would not hold a property in a town that has no jobs and is declining unless you see something on the horizon.

The investor needs to vet the sponsor for track record, property selection, entity structure and operating agreement terms, planned exits and time horizons, etc. to get comfortable to make a decision to move forward or not. 

If look at overall returns those, cash flow + appreciation hands down beats just cash-flow (think midwest) when you're talking long horizons 20+ years.