And like any person running a business knows, gross revenue doesnt equate to how much I make. 

We frequently hear investors chasing properties that meet the "1% rule" which in my opinion is a  flawed underwriting practice (have posted on that very subject a few times in these forums), but in order to achieve a 14% cap rate your Gross Operating Income must nearly meet 2% of the assets cost assuming your operating expense ratio is at 35% (which is very lean on operating expenses).

I'm in escrow on a duplex, my credit score is high 750+, I'm a W2 employee, and I plan on keeping this duplex for more than 10 years.

Considering that DSCR  = NOI / Debt Service and NOI = Gross income less operating expensesWhen institutions are looking at operating expenses for a new purchase, how are they calculated?  

I would tell you to get really, really smart on self-storage, mobile home parks, or something that can be run by a low-skilled employee and pretty hands-off. 

Quick rules of thumb on an ADU return on investment, can you achieve the 1% rule with gross rent?

California charges a minimum tax of $800 a year per LLC, and more if you have gross receipts in excess of $250k.

If your debt is student loans at 6-8% interest your best bet is to pay them down/off as fast as possible as most investments will achieve a similar result but that is gross (before taxes) not net.  

This method saves time and keeps a record of everything you or your employees ever told them. 

I took my duplex from $2,450/month gross to $5,800/month gross.