Based on the value of a property you can likely get away with a inexpensive desk top study such as condos and you will require a more comprehensive engineering study for larger properties like a 4plex.Desktop / modeling options are sometimes good for smaller residential like you mention. 

When considering a Cost Segregation study, here are a few things to consider:https://www.biggerpockets.com/forums/51/topics/1206189-cost-...Feel free to reach out with questions!

Study disqualified parties and prohibited transactions.  

If you haven't done so, you may want to get an estimate for a cost segregation study on these units.

@Brad Herb - one thing to watch when investing in a syndication with an SDIRA is the highly trumpeted ROI in early years via a cost segregation study and the accelerated depreciation it creates...which you'll not be able to take advantage of via a SDIRA.

Purchase Another Investment Property and Utilize a Cost Segregation Study:When you reinvest in a new investment property, you can perform a cost segregation study to accelerate depreciation.

Study the market.

I recommend you really study your market to determine the appropriate rent rate, then market yours 5-10% below the competition for a six-month lease.

It takes a lot of training and continuous study to stay on top of tax law, especially with all the changes in real estate tax rules.

The feasibility study happens here before any filings occur with NYC DOB.