A property with good cash flow can be held indefinitely (even if rent reduction is necessary to maintain occupancy).

That way, you may keep your monthly cashflow and increase even more passive income.But this only works if you are having positive cashflow after deducting all the expenses of maintaining the houses.

It is most common to simply allow this to happen, maintaining original lease language with annual rent increases, as opposed to resigning new leases every term.

Factor in taxes and commission when selling it and costs associated with buying a new property.On paper STR look like they are cash cows, but there is a lot of work that goes into them and expenses/time maintaining them. 

The other 10% of our properties are with a second, or back up, property manager just so we maintain a second relationship.

What about funds to maintain operations?

As many have already mentioned it isn't as hard to maintain as some would tell you especially considering when it's your personal residence.

And I would also add that you want to maintain strong relationships with financiers (banks, private lenders, etc.).

Older home, with 70's era feel but clean and well maintained. 

That, and the added responsibility of maintaining the units and keeping them filled can prove to be quite a leap for a tenant willing to become a tenant/buyer.