The adjacent streets/neighborhoods the houses are circa 1970s and very well kept nice lawns.

Municipality to find out if it is permissible to develop on the adjacent bare lot (may be requirements as to total lot area that prohibit) and if a variance or any other legwork would be required. 

Hello BP community, so I have been lurking for a few weeks at all the posting and advice on the forums and have finally convinced myself that in order to maximize earning potential on a property I have been holding for a few years now I will have to convert it into a multiplex. the details are as follows:currently, owe 120K @ 4.7% 6300 sf ranch style SFR, it is built on two residential lots (room to add a duplex adjacent to this property)currently brings in $1650 for rent, have rented out as high as $2000 (the Eagle Ford shale was booming a couple years ago)have been slowly upgrading and improving (new roof, new laminate flooring, some lighting fixtures, new paint)needs to be updated this was built in 1990, windows are old, some of the siding looks weathered and the worst part is the bathrooms are dated (everything is functional)I have looked at housing rents and most 2/1 or 2/2  usually command $900-$1300Appartments are a little bit cheapper $700-$1100I had trouble using the rental estimator calculator, then tried the BRRRR, I linked the report estimating the following:https://www.biggerpockets.com/calculators/shared/1083149/4f695ede-d602-47bf-a183-b0d69ff0cf64Upgrading showers adding new back porch deck (for access to upper units)converting where two new upstairs rental units would have a kitchen, 2 baths, and 2 bedrooms (comparable to an apartment) about 800 sf ($ 1200 per unit)lower dwelling 3000 sf could be split as well or rent out @ 1500 (would update and add one more full bath) making it 3/2 and 1/2 very large dwellingAll bills paid (water, sewer, power, lawn maint) about 1K per monthPlease review and point out flaws, mistakes were made but so far all on paper and in process of cash out refi, to pay for this conversion. so far budgeted $65K. advice appreciated. more details as required

Anything around Midway Airport and within 35 mile radius or so.Also, Is there a way to find out which zip-codes have the lowest property taxes ?

They are all adjacent to the property. 

Near BWI Airport

Monthly meetings are the 3rd Thursday of every month at the Greensboro Airport Marriott, where we focus on education in various areas of real estate investing.

If the duplexes are adjacent to one another and the total amount of units is over 5 than the lender would most likely have a commercial appraisal done weighted mostly towards the income approach value.

I.e. only looks at issues on the parcel and all other adjacent potential RECs are identified as Environmental Business Risks. 

It's adjacent to the JW Marriott and Ritz Carlton Reserve and Residences, gold course and ocean views galore.