Those are what hooked me originally and I have analyzed hundreds of properties since. a 4 unit would probably require a lower acquisition cost than a 5-6 unit due to residential vs commercial loan requirements, but there are some of both available depending on where exactly you are looking to invest.

I can then find another good deal- used vehicle for below market value, with lower miles, and a bit newer. 

It's extra work/headache for a potential buyer down the road if they ever want to refinance or sell plus it could be a potentially higher interest rate and down payment requirements so this in turn should make the market price lower than typical condo prices but shouldn't be a deal killer as there are plenty of community banks to shop around.

However, when I do a property search on the tax assessors website, many times the Fair Market Value listed by the county is much lower than the properties list price?  

It's an 1700 square foot home with 4 beds and 2 full baths in the lower unit in turn key condition. 

I requested the lender to explain it and stated that they are not sure why it was quoted at the lower rate but the actual amount is the increased rate. 

I have a duplex that has long term tenants in the upper unit and the lower unit has been short term rental (Airbnb).

The depreciation is taxed at maximum 25% or lower based on your marginal tax rate. 

Allentown and the Lehigh Valley would be convenient, allowing you to see the properties you are buying, meet your team in person, and have a lower price point then Philly.

Have you considered an FHA loan, or other facility that requires a lower down payment?