Leverage magnifies return. 3) The effort involved in adding an ADU is comparable or larger than a rehab associated with a BRRRR.

Since you know what you need to buy it at and an average rehab cost, I would say $50-70k for a cosmetic flip, set the ARV based on the sample you choose and doing comps and ask them if they would invest in a deal similar to this. 

Converting properties to multi-family is considered extensive rehab and those programs are a little more exclusive than the standard bridge loan programs. 

Phoenix is a great market to be able to buy properties in your price point, that can be rehabbed so that you can't rent the property for more than before.

I think that rehabbing a property is no small feat, especially if you're trying to maximize your budget.

If you can rehab and refinance (BRRRR) to extract all investment and achieve neutral cash flow you would have infinite return (most of my RE investments have achieved infinite return but the cash neutral has in particular gotten a lot more challenging when the rates rose starting Q2 of 2022).Any money extracted via a refinance is tax deferred. 

Purchase price: $70,000 Cash invested: $60,000 Sale price: $70,000 Have under contract for $70K and will rehab.

Did you have to do much rehab?

The other part sounds like it was a rehab and now held for sale, which does not qualify for 1031 Exchange treatment. 

If you learn how to use Hard Money loans properly and how to find good deals in need of rehab, there are plenty of areas of the country where you could buy 3-4 rent properties in solid middle class areas with good cashflow.