If he must attempt to get the low interest rates of 2021 on this deal, I suggest that he instead look for assumable loans.

Now, after doing this several times my success rate is around 1 out 5.   

All messaging said "soon", when generally there would be some sort of notice or indication things would change. 

For all methods you would want to find a market that has strong employment rates, strong income rates for the market, and is a growing or an established market. 

That worked well when rates were 3.5% but that "strategy" no longer exists.

The house is a new construction in a Class C neighborhood.The tenants pay late rate ~50% of time, they damaged part of the garage, they have people not of the lease living there, and they leave trash in the yard.Part of me wants to keep these tenants because:-They do pay eventually-I don't want vacancy-The turnover costs could/will be high-How much more damage could they do?

Your existing low interest rate mortgage is an asset that you likely won't get again.To Your Success!

Jung,Welcome to the BP forum its a great time to start as mortgage rates fall and home prices still priced well in many states.

I've also held of holding properties in individual LLCs that are owned by one S corporation, which allows for a 60 / 40 split between ordinary income (regular tax) and dividends (capital gains tax rate).With the goal of minimizing taxation and liability protection, what would be the recommendation from more experienced people here?

Many investors start their journey by diving into individual distressed property deals, but if you want to grow into a high-volume operation, it’s essential to change your mindset, strategy, and execution.