@Mike Levene cost to build per square foot is $200-$300 depending on finishes.So, you can start with that.

Option 2: Electrician recommended mini splits - said 2 units should do the trick and would cost around $6-$7k.Heating system 2 is forced hot air oil furnace specifically for the 3rd unit.

We used to hire a company to balance the chemicals and my costs were almost 2K per month.

@Dhruv Patel I believe you are getting ahead of yourself....Where in the US are you all-in (land acquisition, soft costs, hard construction) on new construction multi-family for $100/ft.

The seller offered financing with 20% down, which I used to buy the place.After starting construction and realizing it was going to cost more than expected, I approached a small local bank that knew the property and would offer the rehab financing. 

Rentrange costs the manager to run each report, so as long as you do not abuse it or send the PM 30 properties I would help you.

Would you rather set it and forget it and not need to refi again or rather take advantage of low/no closing costs on this loan and plan to be more aggressive on your rate at the time of your refi?

Finding durable products at reasonable costs. 

How much did the rehab cost and how long did it take to complete?

The challenge with unsafe areas is (1) potentially higher cost of maintenance such as broken windows, etc. and (2) this is by no means meant to be discriminatory but anecdotally from people I've spoken to the challenging tenants tend to be at the lower price points.