They develop, they build, they finance, they property manage, they will have HAO, cleaning crew etc. etc. etc. so the subsidiary companies make money every step of the way.From investor perspective: The investor pay $15 K to reserve the right to purchase 25 multiplex over the year of next 5 years. 5 each year.

Why pay off the mortgage early? 

Show Financial Stability- Proof of Income: Military pay provides a stable and reliable income source that banks value.- Creditworthiness: German banks assess your financial standing, so keeping accounts in good standing is critical.4.

Step 2- close and start rehab-- would need to pay holding cost during rehab?

15% down with no STR experience - you're going to have to pay a price for that.

Keep in mind you will probably have a deductable to pay first.

Now, I'm imaging a scenario when every one of these tenants move out that I'll be paying their entire security deposit + interest even if there are damages beyond normal wear and tear. 

Your son is likely paying more than the property is worth, by definition, as the seller would almost certainly prefer a similar offer that was not subject to. 

It's properly leveraging (not over leveraging) the asset that pays off.  

My goal is to offer an affordable monthly payment that competes with renting a comparable property and offers a benefit to paying a bit more to "own".