If you are syndicating or partnering with other investors to fund a Sponsor's deal and you are a company doing this (LLC, partnership) then get a PPM attorney and file with the SEC. 506B is easiest but if it is really risky...then 506C is best. 

Rent growth has a larger impact on long term cash flow then initial cash flow.I am confident that on a 10 year hold, the higher cost market BRRRR in most markets will out perform the lower cost market BRRRR. 

They asked me to empty my savings, max out cards and then finally to take out a loan.

If yes, then purchase the property.If not, do not purchase the property.

So, comps can help with figuring out local cap rates, then you need the income from the property to determine a value.

Then you can read a more in-depth book like The Book On Rental Property Investing by Brandon Turner or The Unofficial Guide to Real Estate Investing by Spencer Strauss.2.

investors can figure on 10 to 12% return on PMLs   generally they are short term 6 months to 18 months.. in my 40 plus years at PML I find most investors started as landlords then tire of it and start to diversify.

If it is last rental rate charged, then you may have to get creative to accomplish what you want to while still working within the law.Here's an idea to explore.....If it is a 10% increase over the last rental rate you charged, consider using a step pricing lease if allowed by your state. 

Man, Bed-Stuy was rough then.

Feel free to reach out and if not then good look furthermore