If you don't have a background in renovations / project management / construction I would recommend you leave "deal" alone.

Maybe you could contact a local STR management company and work for them for free to get some idea of what is to manage a STR.

If you are scared of losing everything and that everything is the 16k entry plus closing costs, it's not worth it on subject-to which has to be done correct and requires a lot of management to make sure their loan does not get called.

Local Property managers and realtors are a wealth of knowledge. 

Manager said when they replace unit they replace flue because shape on new ones is different and/or Dept of Bldg and Safety require it.  

Since you are investing in areas with lower or no appreciation you will see your equity grow much slower than markets that have appreciation as all you have is debt paydown.If you can leverage your position now I would look for properties where you can create equity through renovations, management, property use, etc.

You didn't even mention tenants who don't pay rent, evictions, vacancies, HOA violations, the consistent rise in taxes and insurance, bad property managers, and the many other issues that cut into your profit. 

We've developed short term property management software based on automations taken from guest messages.

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

The detailed cost segregation study report can help businesses more effectively manage their assets.If assets don’t fall into one of the examples above, there are options such as a 1031 exchange, gifting them through a trust or other advanced tax strategies to avoid depreciation recapture.