Great post I do believe a lot of people under estimate the COST of holding real estate. 

For me when I'm estimating rental income I start by looking at the area for active listings <40 days old with similar characteristics to the home you're looking at purchasing (trying to find same bed/bath count, and same amenities like in CO homes with a fenced yard do very well because everyone has a dog).

Calculate the After Repair Value (ARV), or the expected market value following repairs, and estimate the expenditures associated with those improvements.

He informed me that the auction would happen in 10 days, so he needs to sell right away.ARV: 2.5M - 2.6M Repair estimate: 180kschool zone: 9/10 rating a very popular school zone for the area.he owes 700k in areers!

Step 1 is to get an estimate of the amount of tax deductions that may be available through Cost Seg.

Second, you didn't mention how long they estimated it would take.  

Get fee sheets or loan estimates from whichever 2-3 lenders you're considering and make an apples to apples comparison.

I am working with the city for approval and have a cost estimate from someone I know of 250k to build another duplex on the property and eventually multiple duplex.

As long as you're financing it as an investment property you should be able to.You might have a hard time getting a lender to fund if you don't have rental rates/estimates to provide to the lender.

I did check airdna, mashvisor, str mgt company estimates, etc, prior to going str and I think I was pretty realistic.