Under Denver's Airbnb laws, those would be treated the same as any other kind of rental on the property where you live (whether that's a different kind of basement apartment/mother-in-law suite, a carriage house, or just a room rental STR).

How did they treat the costs associated with the grounds apportioned to the carriage house?

It's okay if it's in a basement apartment or carriage house while you live there because those are considered accessory uses to the primary use and not a second unit.

Replace the garage door with something architecturally appropriate, like a carriage house style that looks like four individual doors, and paint it to match the house.I think you'll be very surprised at the transformation, at less cost than removing and patching.

More specifically, my home falls under some of the most favorable zoning within West Hollywood, allowing for up to 5 condominium units, 1650sf each, carriage-style. 

I had a similar situation in Savannah, GA where I bought a triplex which had a carriage house.

You can rent out accessory units to your primary residence (a carriage house, an attic apartment, etc), but you can't rent out the other side of a duplex.

I have an equity-out loan against the property holding both houses (I guess it would be called a multi-family property, although technically it is on one piece of land, including a main house, a carriage house, and a free standing garage), for about 70% of it's value, but otherwise I hold all of the equity in the remaining properties.I guess right now I am at a turning point in my desire to actively pursue this as a full-time profession.

In the last 150 years we've managed to come from a Horse and Plow to a John Deer, from a Horseless Carriage to an Automobile, from a Bi Plane to a Super Sonic Jet to a rocket to the Moon and back, from the Mayflower to the Queen Mary II. from Black & White TV to Big Screen 3DHDTV, from Super Mario Brothers to an MP3, from a "Big Momma" IBM that took up a square block on Wall & Broad to a tiny IWatch. 

I got my second property as a triplex there(duplex with carriage) and have been enjoying the profits of that.