Can you make improvements  in the carriage house and see an immediate return? 

If you plan to Airbnb the extra space, be aware that the city of Denver seems to be cracking down on basement-unit and carriage house STR setups.)-- If you like the short-term rental model, be aware that at least in the city of Denver, it has to be your primary residence.

You might find out that that century-old carriage house in the back yard was built using 17 different kinds of asbestos.  

Whoa, whoa, whoa...back up the horse carriage.

Right now, we have a tenant in a separated carriage house on the property, who pays rent @ 1100 per month.  

It is in the "Pocono Farms East Carriage Estates" development, which is supposed to be a good development.       

(Whether it's in a house with a basement apartment/carriage house or just renting a room.) 

Lots of properties with mother in law suites and other accessory dwelling units called “carriage houses”Use https://landlordy.com/ to manage the house hack and it will make your life so much easier.Feel free to reach out if you have any questions!

They have heard of the "horseless carriage" but have their doubts as to its reliability and difficulty in learning how to drive it.

Word of caution they wont allow you to use the future income to qualify going in, but will allow you to get a partner or co-signer.https://www.denvergov.org/content/denvergov/en/denver-development-services/home-projects/building-expanding-a-home/detached-dwelling-carriage-house.htmlGood luck keep us posted