Also, in our experience, 95+% of agents have no clue how to calculate ROI, Cash-on-Cash, Cap Rate, etc., so what are they really going to help an investor with?

Just make sure to consider PMI (private mortgage insurance) in your calculations since you'll be putting down less than 20%. 

Curious what's the advantage to calculating it per unit instead of the building, TY

Calculate the potential cash flow and return on investment to ensure it aligns with your financial goals.Purchasing a duplex and house hacking: This option offers the advantage of living in one unit while renting out the other, potentially covering most or all of your housing expenses.

Is “purchase price” $350k or $50k when calculating for some of these analysis metrics?

One of our staff would calculate interest principal hand write it in the book and mail it back.. that went on for 5 to 7 years which were the terms of our notes.

Maybe you can calculate proper lawn watering costs and give the tenant that amount as an allowance.

BiggerPockets also has a calculator you can use to analyze deals and I highly recommend you start this as soon as possible, even if you are not ready to buy.

I read the book Rental Property Investing by Brandon Turner, did some research, played with the buying calculator and rental, listened to some podcast.

Given this scenario, how do we calculate the penalties, and how much does she need to pay in penalties by the next rent due date?