Many of them charge 25% or more of gross revenue.

Doesn't matter what the neighborhood is......I've seen fully occupied triplexes in East Oakland going for 600K and the gross rent is only a total of $2,200/mo and the seller is wondering why nobody is buying because it's such a "great price".

Specifically, the 3% interest rate, $5,500 in up-front repair costs, $2,000 in monthly gross rent projections, and $180k after-repair value would be a good start.I'm especially curious about the interest rate on the loan.  

If you're purchasing a rental using a non-bank lender, then the lender will use the market rent for the subject property to underwrite the loan and all that's required is that the gross rental income covers your monthly payment of principal, interest, taxes, and insurance.

the gross rents, newer construction and seller financing How did you finance this deal?

Gross rent potential is about $1800 with landlord paying all utilities. 

Imagine making 200k in gross commission and having a broker take $60,000 and even sometimes up to $100,000.

Currently own a duplex just outside Dayton, OH that we bought for 72k, spent about 20k in rehab (over a year or so) and now rent it for $1535 per month gross.

The gross rent is $3,598.63.

There aren't many secrets other than gross income minus expense equals net operating income.