Purchase price 70k currently pulling 900 rent ARV 110 - 140k, rehab about 25k 

Purchase price: $490,000 This is a unique opportunity to participate as a investor in a single family residence valued at $3M and higher.

I purchased a fix and flip that got complicated when we found one of the basement walls was bowing in.

Yes you can find properties which you will be able to purchase, but ROI will be near zero or negative. 

In the next 2 years, I'll be looking to purchase a MFR to househack. with the idea of reinvesting all of the cashflow to help scale.

Are you purchasing as investment? 

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

If purchasing new real estate as part of your reinvestment, a cost segregation study can maximize depreciation deductions, offsetting future taxable income.For effective planning, assess how the sale price is allocated between real estate, tangible assets, and goodwill, as this determines the tax treatment.

For a purchase generally application would be to review an ID, asset statements, and LLC docs if neccesary. 

Keep in mind, it would be in your best interest to go for as high as 4 units on each purchase to maximize your door count.