Some items to consider are accessible path of travel (gravel is not going to cut it), potential elevator, potential historical preservation involvement, and the biggest issue is if a business can garner enough clients to cover the cost and still make a living. 

Is it just preserved since the refinance is just on the remainder of the loan?

Historic preservation is not an issue, so it could be completely demolished and modernized.

It is easy to burn through downpayment money, so I personally like to preserve my cash.  

I imagine someone purchasing this many units can probably just return the faulty ones for replacements pretty easy within the first few years in order to preserve goodwill for future bulk orders.

This preserves the relationship you have and leaves little room for misunderstanding.Congrats on the deal!

Contributions to the 401k may preserve the 20% deductionHow big a portfolio do you intend to grow?

"Core" stabilized assets are for investors with low risk profiles who want capital preservation and stable predictable cash flow with low risk (versus higher risk alternatives in stocks and bonds...or value add and real estate development).REITS, insurance companies, pension funds, family offices, very high net worth individuals/families who have already made their wealth, etc. 

But amazingly, my street is very quiet and has been designated a historical preservation zone.

You're definitely not alone in feeling the itch to get started right now, but be patient, preserve your retirement savings, and use your money to purchase reliable investments in solid areas with a great PM/turnkey provider.Best of luck!