It is recommended to delay any improvement on the property for a one-year period from the date the tax deed is recorded.

So, after whatever is the time period for your state/county, you will need to go back to court with a form letting the court know and telling them their work and banking info. 

There should be timelines for the buyer and seller to perform during the escrow period.....

Some may have minimal rental periods.  90 days is fairly common.   

If you fail to pay and the 30 day period to respond has passed, you may be required to start the process over (my office requires this).

If you sold the 28 houses for 20k each on payments, that equals 560,000 in accounts receivables collected over a 5 year period.

Even if you pay $300 labor and 150 materials each time, but the work is continuous, it can still be considered as series contracts (one contract after another within a period apart, even if you do 1-3 day a week/month, as long as it has a pattern, it could be considered as such), remember that CSLB and CA are pro workers (particularly with workers compensation), you don't want to mess with them just like you don't want to mess with IRS.

Yes $3650 is not a lot of return on rent on a $1.5M home, but how much has the home appreciated over that same period of time? 

I guess the app would tell you if the power dropped to zero for a significant period of time.

Biggest downside is that they have a prepayment penalty, so that's something you'll want to consider if you think you might want to refinance in the next couple of years. 3-5 year penalties are common, but you can choose to buy it down to a shorter period of time if you'd like.