And my wife for the support.The best part of it all is we just found out we’re having a baby girl early next year and we added $100 automated principal payment each month to our 30yr fixed mortgage so that it amortizes when she turns 18 as @brandonturner suggests.I’m so grateful for bIggerpockets and the community it’s formed to inspire and support me through this journey.Next year I hope to do my first BRRR!

NAR/CAR ethics stipulate 'Seller is Agent' disclosure in writing on the MLS etc at time of listing because even if Seller is not the Listing Agent, licensed seller/owner may expect and/or receive compensation (ie, gift, referral fee, portion of listing agent's compensation, etc).Thus licensed seller is inherently not strictly limited to being a principal in the transaction, so would have had to disclose seller is licensed agent. 

Acquired a note that pays principal and interest

With that said cash flow is one piece, and principal reduction on payments is another.

But there isn't a lot of calculation involved, other than figuring out what your payments would be on different principal amounts, and any widely available online mortgage calculator can do this for you in two seconds. 

I get depreciation, principal pay down, positive cash flow of usually about $500 or more per month per property, and the Tenant Buyer maintains the property (so, no toilets to worry about ;-).

You mentioned you have only owned the property for three years so I assume you haven't paid down much of the principal but because you did put work into it, it could be worth getting an appraisal of the new value.

If you're a principal in the transaction you can make any changes you wish.

I was told that instead of usuing the 3.5% down loan it is better to use a 5% down type loan becuse more if your money goes towards the principal that Way.

If you are on the get rich slowly track (depreciation/principal paydown/rent appreciation), I'd probably do it.