Could always get lucky and sell to an investor who pays higher, or it appreciates faster as it becomes more desirable with density increases.

I bought 1 House out right, I am refinancing for 100k. had 1 renter paying 1000. using the refinance to purchase the second property, and putting renter for 1400. it will also need 25k in repairs.

Trying to figure out what I can/should expect to charge for 1)Purchase price; 2) Down payment and; 3) the spread per month if any on what I pay per month.

There's very little way to go wrong here since the alternative is paying to live somewhere else anyway. 

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? 

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

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.