You can also discuss properties for sale with the PM you plan to use and get up to speed on expenses and operating issues you need to be aware of.Bottom line you ned to become an expert. 

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. 

The only way you'll know the extent is to hire a plumber to evaluate the entire system and be prepared to spend a pretty penny to bring it all up to speed.

It gave me an idea of both price point and what I could expect regarding occupancy rates.I also invested a good bit in the quality of the build out so I’d be competitive for the best guests looking in the area and get ranked as a super host… that gives you an advantage in search results.

For considering deals, your buyers are going to want to know stuff like repairs that need to be made, condition of major things such as roof/HVAC/plumbing, property ARV (After Repair Value), a few comparable properties for the ARV you came up with, and plenty of quality pictures of the property.

If you’re working with a quality agent who values their reputation, I would use the inspector they recommend over some random one for sure.