Relatedly, the estimations of closing costs seems low - it seems the consensus is to budget 5% of the deal cost for closing costs.

For $50/month we get to deal with rigorous screening of less than ideal tenants, constant calls from tenants, damage to the property every time we turn around because people do not care about things in this class of property, Section 8 and the government (who doesnt love to deal with the governement), maintenance requests because none of the plumbing is updated, codes enforcement because the tenant decided it was a great idea to put a couch in the yard, and last but not least angry owners wondering why their pro forma isnt being met ("I was gunna get a 75% COC on this thing").Now this is a pessimistic view of what it is like but PM is a pretty thankless job, especially in low end properties.

Your numbers seem low to me, but I'm from NY so I expect to see much higher property tax rates.

You couldn't buy a 5-unit with a low-downpayment owner occupied loan.

This is where a low low low ball offer is appropriate. 

When you make a low-ball offer, you might worry about making the seller mad by offering too little and insulting them.

The property taxes are low for California.

You did not include Vacancy reserves, Property Management, and your 3% for both CapEx and Repairs are too low.  

Anyway cap rtes are thrown on here frequently and the way theya re defined on here befuddles me as I am used to the Walgreens / Targets of the world and ( typically A+ tenants in the 5 range A Multi family will get you high 6's low 7's in various markets ) cap rates determine value  eg...

A low fixed rate conventional loan just sits there and pays down quietly, not spurring action.