Unlike traditional real estate notes is something that is easy to do from afar since you do not get access to the interior anyways so there is nothing you can physically inspect.You are correct that you will get $500-$600 a month in payments but also recognize its taxed at ordinary rates... 

My sister is selling her house to me; however, we want to do a mortgage transfer since she currently has a 2.5% interest rate, but the bank will only pay what is owed on the current mortgage.

You should research STC rating options.

And only private money should be taking a percentage of the profit at a lower rate.

This avoids the seasoning period and still allows conventional financing for the best rates. 

MLS, negotiated 12k seller credit for rate buydown.

Well Erik, I received 3% seller’s credit to buy down on interest rate.

Just know if you want low money down and you do owner finance/subto/lease options, you will need to do direct to seller advertising and have a good real estate attorney.

Most markets in Florida are quite lucrative and have higher and consistent occupancy rates year-round because of the weather.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.