Sounds cliche but always best to reach out to a trustworthy loan officer and fill out an application because there are too many things to look at before determining how much you can qualify for. 

Lenders often consider a percentage of that rental income when assessing your borrowing capacity, which could make it easier to qualify for a new loan.Market Conditions: Analyze the real estate market in both your current area and the area where you plan to buy.

You'd just need to check with the lenders what they allow up to.Having experience (completed rehabs in the last 3-years tends to be what most lenders look to qualify as experience) will help you reduced your down payment all the way down to 0% in some cases for extremely experienced investors.

You'll get a few advantages from higher loan amount (qualifying rental income)  to substantially more income (multiple units).   

Are there any lenders offering HELOCs for small business owners who primarily use bank statements to qualify, especially those with write-offs?

From what I can tell, it lets investors buy a property that probably wouldn't qualify for a conventional loan (these properties were...not livable). 

It's a high risk area, I would expect a lot of turn over/vacancies before you come across a qualified tenant.

The IRS expects your cost seg report to be "factually intensive", "supported by corroborating evidence" and performed by a "qualified individual.”

From how you describe your situation, I don't think you'd qualify for the construction loan, they are very conservative on their underwriting.  

Talk to a lender immediately and see what you can qualify for.