What makes a “good” deal can differ enormously from person to person.  

If the property is paid in cash and later a mortgage is secured does it impact the UBIT question above ?    

Additionally, how will it impact the sale prices?

What's most impactful about truly learning neighborhoods is the ability to identify a "C" neighborhood that has the potential or is actively becoming a "B" neighborhood.

While renovations and other expenditures can be capitalized (and in some scenarios deducted) when you classify property as a rental, that might not be a significant impact if you intend to sell the property soon and can qualify for the 2 out of 5 year deduction for primary residences. 

One thing I didn't mention earlier, but came up again is the impact of CapEx savings.

Of course, the Federal Reserve's QT also impacts the supply side and can cause price changes that are not one-for-one with changes to base rates like the fed funds rate.I find it so interesting that you can have spread widening at times when rates are going down.

Reach out to the local tax assessor to understand how a sale might impact your future property tax bills and reach out to an insurance broker to get an insurance indication. 

Make sure you know the impact that adding an ADU will have on any rent control.  

The more leveraged secured debt you have will impact any cash flow.As mentioned by Nicholas, the BRRRR method could help payoff the HELOC too.