There are way better returns to be had in the market for a similar amount of work.The only other thought regarding keeping the property is what the condition of the property is and if he could upgrade it and get a significant increase in equity position before he sells. 

Generally speaking, if your investment upgrades or adds to the property, it is a CapEx.

For example, there have been a number of times my tenants have had trouble figuring how to work the thermostat and so wrongly assume it is broken.

., cleanliness, basic landscaping for SFHs, holes in the wall, doorknobs broken, etc.).

If yes, what would you recommend I do if broken down in steps?

It seems as if there will be some upgrading of the units, are you anticipating a sale or refinancing out of the subject to different mortgage afterwards or is that the long term debt instrument you want to keep?

The only people still crushing STR are the ones who are upgrading their amenities, services, and ambience.

Have a checklist and check it off one by one to make sure you don't miss any upgrades you have made.

Avoid Over-Improving:Avoid making luxury upgrades that don't add significant rental value.

I'm trying to grow my portfolio, so my money is spent either on new properties, or upgrading existing one's.