There are a few dozen houses with my target number of beds/baths/sqft that have been listed for rent on Zillow for 2+ months with 0 applicants.Is this normal or is it a sign that's there's not enough demand for rentals?

Most list on Street Easy. 

. - there is a airbnb in my street which seem to have good occupancy Thanks in advance for all your suggestions.

Here is a fantastic website that gives you a LIVABILITY score for each zip code/street.

We manage a portfolio of 500+ units and the most common duplex you will find in the area is an up down that has 2 beds and 1 bath per unit, your looking at $600-$650 a unit for those. 

I am closing on a 4 plex in Bridgeport, all units are 2 bed 1 bath, and the current rents are under market at $600 against a fair market rent of 1200+.

Does providing complementally k-cups/teas, popcorn, spices, toiletry essentials (toothbrushes, floss, bath wash, shampoo, conditioner, soap, paper products, makeup remover, laundry detergent, firewood with firestarters for the fireplace and firepit constitute as substantial services?

The market, as in wall street, politicians, the media, would tell you things are great.

Each unit is 2 bedroom, 1 bath.

My buybox is <150k, as turnkey as possible, 3 bed, prefer 2 bath but will do 1 bath for the right deal, neighborhoods with lower crimes than the nearby areas, rent at <1.5k.