I just purchased my first duplex (only SFHs in my portfolio so far) and it doesn't have the gas/water split.

If you are looking to just calculate profitability, set how much profit you want to make then:ARV - Purchase Costs - Holding Costs - Selling Costs - Desired Profit - Rehab Budget (including contingency) = Maximum Allowable OfferIF you cannot calculate those numbers, a spreadsheet isn't going to help you. 

Purchase price: $360,000 We bought this stacked duplex, lived in one unit for 2 years and moved on.

Sandra For transparency purposes, I believe you meant to say that you purchased a turnkey property from Memphis Investment Properties, not Memphis Invest. 

Purchase price: $110,000 Cash invested: $45,000 Recently purchased my first house to use as a primary residence, currently I am renovating the kitchen and adding a full bathroom to the first floor.

The substitute of collateral was more of a scenario where you sold for $155K, and instead of paying off the $88K loan in your scenario, those funds stayed at the title company and were used on a cash purchase happening nearby in date. 

Purchase price: $90,000 Cash invested: $60,000 Buy and hold that I still have to this date.

Santarelli allegedly purchased from a government auction from the bankruptcy trustee and relaunched online.

Current timeline to purchase is probably 6-12 months as I start narrowing down and visiting some of the places to get a better idea over the next few months.

What this leads to is higher purchase prices but also higher rents in these areas.