However, by extending my search to areas beyond, such as Riverside County, I found that $700,000—or perhaps even less—could secure a 4-plex.

You may not include income earned that is not on a tax return, an administrator or PHA may consider additional income in that household, a teenager may mow lawns or receive child support that may influence funds available to that household. 

After they pay rent and taxes they have about $1,500 or $388 a week for everything else.

Being able to 1031 it into something larger would pay great dividends down the road, not to mention starting a fresh a depreciation cycle on your tax cycle. 

What is the tax treatment with respect to reporting, depreciaiton, etc.

But considering all the expenses (PM, leasing fees, cap reserve, maintenance, taxes, etc), it has been showing as negative cash flow. 

What is commonly known as DSCR Loans are loans from private lenders, not typically banks, and these loans are part of the "Non-QM" umbrella and turned into mortgage-backed securities, not typically held on a bank's balance sheet.Here are some articles published on BP that should help!

HM lenders, depending on the lender, want to make sure you are using your cash and not borrowing money that isn't collateralized (secured by real assets). 

Tax benefits, good investment possibility, cashflow.

One thing to consider when you are budgeting is the taxes and insurance.