Cash-flow is a defensive strategy at best (I don't find it very reliable; unexpected CAPEX, vacancy, etc.). 

Compile a punch list of any incomplete or unsatisfactory work, and ensure the contractor resolves all issues before making the final payment.Obtain and retain copies of all inspection reports and permits for your records.Collect warranties for any new appliances, systems, or major components that have been installed.Provide feedback to the contractor on their performance, which can be beneficial for future projects and maintaining a good relationship.

Source: https://leginfo.legislature.ca.gov/faces/billNavClient.xhtml...Always consider the tenant management component of any changes, however.

Include a contingency budget for unexpected issues.

Your most critical component is a great cleaning service.

I will say that I have received assists from appreciation on all my RE investments and some of my refi may not have achieved the infinite return without the assist, but without the value add component the gain would not have been the same.  

-if you have other income sources, you can think about real estate as one component. 

Well focus on market will low expense ratios so that rent (the largest component of inflation) is certain to grow faster than expenses.

Most often older the better actually, because manufacturing process's drastically changed and components have a quarter the use span older components have.     

Sometimes the best opportunities come from unexpected places!