Last property I bought had 8-9 offers.New York has a lot of downpayment assistance grants and loans. 

Use a home equity loan (fixed debt) instead of a HELOC (variable equity) and build an additional unit you can rent out in your own backyard.

I moved to miami and it's tough to do here columbus land is cheap. lower than lenders even require our buyers have to come up with additional equity just to close the loan. not sure austin's economics but happy to look at a case study with you to see if it's feasible 

Some lenders do a periodic search of ownership records of all properties in their loan portfolio.  

There are some HOA's that are in such bad shape they wont allow any type of loans and it must be a cash purchase.

I would look at the DSCR loan as the first option.By the way, I suspect you are going to be disappointed by any refi appraisals   ADUs typically appraise poorly   JADUs can lower the property value Vs having the space as part of the primary unit.  

@Charlie Loomis use Metron meters but do not use their installers.

Here in the USA you need what's called a "construction loan" and it's also very hard to find a company that will insure you if you're a newbie.

30-Year Conventional: 7.01%30-Year VA Loan: 6.40% Drive Safely, Las Vegas!

But would I tell a person I don't know to find and buy a severely distressed property, take out a hard money loan to buy it, perform a monster rehab, and then refinance and hope for the best?