You could read 100 books and still need to learn more because certain things must be learned through trial and error.

@Arun Philipnot sure if i understand your question.if you don't have any cash, period, you shouldn't be buying any more properties. 

Once you've identified what's important and what ratios to look for to evaluate a property, all future deals should be weighted against those "good" ratios/numbers - and periodically adjust to suit your goals.

You could do a full MTR during the period you're gone, but for me the best and easiest way to go would be to just rent the other rooms in the house as a LTR. 

Renting the home does not void eligibility for the exclusion but does require you to account for depreciation recapture from the rental period.

You absolutely want to be concerned with this.I would just argue what you're concerning yourself with today may be totally different in that 10-20 year period.

Although I’ve been investing in real estate, both directly and indirectly for 45+ years, I still get a “queasy” feeling when an investment does not perform as expected.My “aha” moment occurs when we reach the point when, despite the investment problems, we’re able to still show a good/substantial profit at the end of our holding period.  

Quote from @Chris Seveney: If you can borrow private money for that period of time at 10% that is a very good rate.

You could read 100 books and still need to learn more because certain things must be learned through trial and error.

Find the market with the best market appreciation over the hold period and you will have found one of the better cash flow markets over that hold period.As for the forced appreciation….