Then I pay those loans off asap and repeat.

Meaning if you only 'pay in' on say 50% of your income each year by using the S-Corp strategy that you will also only get a proportionate retirement benefit down the road?

You still have to pay your mortgage.

If my boy turned 18 on April 1st - does he escape FICA for the first 3 months of the year and starts paying it from April forward? 

A purchase you made in 2020 or 2022 would not really be thought of as a BRRRR because I'm guessing those units have been rented since then and were not just sitting vacant with you paying on those mortgages.

If there are fines to pay, it’s the LAIC’s responsibility to pay them, if the owner doesn’t.

That depends - if its a short term hard money loan possibly, but expect to pay more for it.I would first ask your current lender if you can extend the loan.

You are a high w2 earner, The house is worth 110k today, you are buying from your grandma for 60k in exchange for free rent for life, upside ARV of 200k.The costs of owning the house will help provide tax relief on your high w2 earnings, you are buying a great chunk of equity that will pay off in the future, and you and your grandma are doing each other solids. 

Prices are around $300K for what he's looking for (total costs around $2000/mo, and income will be around $4439/mo... but if he has 2 roommates each paying $700/month, it's totally doable. 

In that case you need to pay the difference.