I am not an expert at any of these things, but working on projects with experienced contractors has taught me a lot about construction methods, but more so taught me about how professionals operate in the biz.I have also attended architecture school at UNC- Charlotte. 

My background is in marketing in the engineering/architecture industry for the past 15 years.

I have two degrees in Interior Architecture and Anthropology that absolutely come in handy when I tackle a fix and flip. 

Have phase 1 architecture drawings/site plan that have been informally reviewed/okayed by local building inspector.

If you ever need any local architecture / permit advice send me a message. 

Let's say you'll be at $120/ft to build so you're at ~$257k in build costs not counting another ~$10k in architecture and engineering.

The list you have there, assuming the work was completed professionally (architectural shingles, good quality kitchen) and barring destructive tenants (which seems not to be the case) sounds like he put about $70K in already.  

The general character, look and feel, etc. will most likely remain low-income for the immediate future just due to the architecture, layout and demographics. $350k is a decent price for a duplex anywhere in Boulder County, it’s a very entry-level price point.

I do real estate because I have a passion for housing and the art of architecture.

Some of the differences with SFR that make them less valuable than otherwise similar comps are location on a busy street, smaller lot, bad condition, structural defects, higher tax area, different school zones, different deed restrictions, access to main roads, rush hour traffic, obsolete or unpopular architectural style, inferior finishes, time since remodeling, age of roof, flooring, and others too numerous to mention.To get the discount to fit your formula, you’d probably need to find a house needing significantly more than $15k of work.