I am interested to learn about 1031DST Sponsors size and quality:
Size, capital under management, credibility in the industry. Some top 5 or 10 list is good.Front-end load percentage, Management fees.Capital Gain per...

If you're worried about quality I would ask your plumber if he has a recommendation, typically they will have a back up option available. 

I have no outstanding debts outside of my current mortgage which is $156k Just refinanced with a 30 year.

You really get so much in RE by the quality of the relationships you have.

Each will have their own underwriting criteria, but categorically they will be looking at your experience and financial situation, along with the quality of the subject deal.The 'Network' tab on BiggerPockets is a fine place to start sourcing HMLs.I know organization is important when approaching lenders, so I'd most likely make an analysis to show the lender.Not sure what you mean by 'analysis', but this isn't likely to affect the lender's underwriting decision.

Quality of finish, zoning and code rules? 

You probably know this.Basically, invest in the top 10% quality of that City, and you'll probably do fine.  

A quality investment will have enough NOI to service any loans on the property, cover expenses and taxes, and have enough leftover to pay you back on your cash investment. 

. - "I want to buy a duplex in Denver, CO in a great location and maintain it well for decades because I believe that a property in a desirable location in my city will only increase in value over time, as long as I treat it well and place quality tenants.

I am fairly handy, but I want to buy in a good neighbourhood that will appreciate well and attract quality tenants.I am assuming it would be very beneficial to speak with a local mortgage broker and real estate agent that specializes in real estate investing, but don't know any.