The idea of having a cash flowing portfolio large enough to reduce or even fully step away from my regular work is obviously very attractive, but as a total beginner I don't want to set my sights too high without first gaining some experience in REI.

I've done many out of market flips, quite a few sight unseen.

Last year my accountant said he would only have to pay the capital gains on the portion of principle he received each year.

Distance between entrances, sight line distances down the road, culvert requirements. 

In the meantime, we have set our sights on a different geographic location (also in the same state) for our retirement, and trying to figure out the best strategy to afford to ultimately purchase a property there.

Do you have a good relationship with your neighbors and would the RV be hidden or in sight? 

The same principle.

This is easy in principle, but difficult to pull off.

For example, interest only vs. interest and principle vs. interest, principle as well as a certain minimum % of the loan are all types of payments I've see on lines/loans of credit.

So, typically you as a principle have to personally guarantee the loan.