In the residential world, some requirements are relaxed comparing to commercial so it's up to you whether you want to spend the money to have a better planning versus skip the planning and perform the work impromptu.

New builds typically tend to appreciate faster and demand a higher rent than average for an area compared to older units (we often see a higher quality tenant(s) in new builds as well).If you were to buy an already built 4 plex are you expecting any immediate or mid term rehab and what are the projected rent rates and rough estimate for annual appreciation.

If you buy a package of 6 lesser houses  that means I have 6 roofs, 6 hvac, less cashflow, and likely subpar appreciation(dollar for dollar) compared to better areas.The reduced maintenance costs, higher rents, better tenants, appreciation, and reduced hassle factor for new construction are real and attractive.  

But with our market and projected rental rates compared to our mortgage (with 2.99%) we decided the purchase price for a new primary would be more costly down the road than another rental. 

Salem, for example, often offers better cash flow opportunities compared to Portland.

We recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

Back in the late 2010's, Philly had potentially due to the low tax vs the comparable rent.

But there is still some meat on the bone from an appreciation perspective compared to other developed ski resort areas in CO like Breckenridge, Avon/Vail, etc.

If my property has 4 units (2x2bed/1bath and 2x1bed/1bath), I need to look for the similar quadplex within 1-2 miles radius to compare.

You're probably not seeing Orlando as a place to invest because it's difficult to cash flow compared to other markets.