Do you typically have a separate bank account for each property or do you have one main operating bank account? 

Like @Russell Brazil said there are general things that need to be in place.One that stings a lot of people is the main entrance door.

The higher credit is attractive, but what if the couple's income is 3.2x the monthly rent and the single woman makes 6x the rent?

I think it's going to be location specific for sure; where I am very few people hang out in the house all day long as they are usually busy hitting the parks and attractions. 

We plan to rent out the main house and ADU in the future but also concerned on the return if/when we do sell. 

You can find them through local real estate investment groups or online platforms.Auction or Estate Sale: If the property has unique characteristics, especially being a large, old Victorian, it might attract specific buyers looking for such properties.

But your main killers; road access, water access, fire hydrants, flood plain, storm sewers, Storm ponds, road surface requirements, etc. 

I worked for a property management company that requires all potential tenants to check into the main office prior to showing as a means to provide a safe showing for the employees.

The ROI is attractive at 16%, but ensure ARV aligns with recent comps given market trends. 

You could be in an expensive market, like LA, but you inherited a property or you got a killer wholesale deal or subject to and the numbers could be very attractive compared to buying off the MLS for full market price in the same market.