As far as the other property, my ultimate desire is to build a duplex for rent. 

I decided to keep it as a rental the last second and is currently rented for $2,250.

We are wondering if it would be worthwhile to buy a home instead of renting. 

Brandon You have to get out of Suffolk County and start looking into other areas where you can still get a good deal and the rents offer a positive cash flow without having to put 30% to 35% down. 

We currently own two rental properties (details below) and are ourselves renting a place to live in ($2350/month).

You could have a few things driving the cost:-Location - if the house is more remote the contractor will have higher costs to get out there (gas, lodging, limited resources) or if you are using a local guy he might be higher because he knows there are fewer competitors -El Nino - the roofers we use are all busy because people are rushing to get work done before the rains hit.  

I want to provide several locations, and it increases the likelihood that they will reach out me, and a higher chance I have availability. 

Can they prove how long it takes to rent a vacant property?

A place like Austin, TX has been over built and rents are going down and vacancy rates are going up vs. a small market like Reno, NV the rents are increasing because of a lack of supply and driving appreciation and prices up. 

He is month to month so all I would have to do is give him a 30 day notice of rent increase.