Note that the cashflow number you estimated seems a bit on the low side, but that'll depend on how accurate your estimates were.The duplex option doesn't seem like a great deal just based on how you described it - sounds like it's just listed at market value (at the high end).

1- Is that accurate? 

Pay attention to the condition of your property compared to the comps for a more accurate ARV.I would get hooked up with a local agent and get a BPO for your ARV if you want more exact numbers.

Everything I read seems to emphasize making sure to accurately and completely estimate your costs up front to make sure you're dealing with a good investment, but so many people's estimates seem to simplify the costs to only recurring monthly and highly predicatable costs like taxes and utilities....etc. 

Given the neighborhood and homeless folks right there. the numbers seem pretty accurate.

They came back to me with one similar comp and told me there was not enough information to give me an accurate estimate.

BUT it is not month to month - it is year to year, and expired apparently on February 28, 2020, and now has a NEW expiration of February 28, 2021 because it renews for a like period - year to year. see this from the NJ Truth in renting:  Yearly and month-to-month leases will automatically renew for another term unless a valid notice to quit is given by the landlord or unless the tenant gives notice to the landlord that the tenant will return possession of the premises to the landlord.If you have in writing a communication from the agent and seller's lawyer that there was no written lease and now there magically is, I would recommend you not close until you verify that you have an accurate tenant estopple letter from all tenants and the information is accurate. 

The other 3 very spacious rooms—2 of which have private entry doors—are directly off of the common area.What is the most effective and accurate report/tool I could use to estimate rental rates by room?

Make sure you have an accurate manual J calculation done so the unit can be property sized.

"It takes 3 seconds for the landlord to do it "We must be talking different things then, estoppels need lessor/lessee signatures - More than 3 seconds.If you're talking about stipulation that a rent roll is true/accurate, then that's not an estoppel.In OR, we don't use estoppels often on properties besides commercial spaces with long term tenants.On apartments, you get a current and mutually accepted copy of the lease assigned to you as buyer to enforce.