Look at insurance and tax costs, those two items are the biggest killer of cash flow.

Without knowing any of your financial position of your work or side hustles it is hard to give you exact advice because you may be able to carry these homes until they are paid off and in that case they would provide solid returns, but there are likely better real estate investments out there.  

You make the payments to the lender.Oh, and just in case, there are more items to know about when considering a "sub to" transaction but this is just a comment on the payment aspect. 

If you are on cash accounting, yes you could do that.On the other hand, you are ignoring carry-forward losses. 

This is just one item. 

At the end i will add a list of items why adding a single ADU in single family zoned areas may not be the best RE option.The most common value add is via a rehab.  

It’s ran like a business, not a personal investment.Given the heavy workload I have being the CEO/founder of the wealth management company, my wife has set up a well oiled machine on the property management side, due to her perfectionist drive however, it still means that she's constantly dealing with tenants and toilets and replying to items at all hours of the day and night.

I could completely be misunderstanding the process, so thank you, in advance, for clarifying these items for me.

I would try to buy properties starting at a specific date so not large ticket items come up.

I like using these for just this case.Another item to consider is since this is a 2nd floor I wouldn't be that worried since the 1st floor will heat the 2nd floor enough to not allow frozen pipes.I would also talk to an HVAC person because I believe they can also put a device to cycle the heat a few times a day or even put a secondary thermostat in the apt to take care of the minimum issues.I feel for you because otherwise you have a great tenant.