So I'm going to start backwards and go from there. To your question about where these cinematic "western" tropes came from, the main source was Dime Novels. These were comic book-esque stories about western culture that ran the gamut from characters, locations, plots, etc. They weren't terribly complex in that the story's hero was always that: a hero to the bone. (The characters weren't exactly layered) They usually revolved around a white man coming into an untamed area (or near one) and saving a woman or family (or idiot) from...well...dark-skinned people. On occasion, there were white villains, but these stories usually towed the disgusting cultural bias of the writers out east who churned them out in a matter of days. Asians, Native Americans, Mexicans, and Jews (perceived threats to Christian civilizing forces) usually swindled, kidnapped, killed, or cheated the "damsel" in distress, and a white male hero rode in and saved the day. It sounds corny and stupid because it is: but really, this was the formula.

Dime Novel writers found that books sold better when they worked in real, notable western figures into the narratives, so people like Kit Carson, Buffalo Bill, and even someone like Jesse James made frequent appearances. Interestingly, social and political shifts altered who could be a "hero" in these stories, so during the economic Panic of the mid-1870s, when people were distrustful of big institutions like railroads and banks, outlaws with hearts of gold became more acceptable in this role.

During this period (1870 - 1899 or thereabouts) the basic outlines of the cinematic western archetype found definition. Although a "cowboy" in the real American west of this period was a person who literally worked with cattle (often called "punchers"), their dress and gun belt rig became synonymous with the western white knight hero portrayed in these dime novels. Thus, when dime novels fell out of popularity at the beginning of the 20th century, the blueprint was already in place for cinema to piggy-back upon. In other words, the dime novels created the look and narrative foundation for more than a century of artistic representation in film. The story beats were almost identical, as was the look: which is the funny part. The people who wrote the dime novels were almost to a man east coast dandies who had never gone further west than Ohio. These people didn't really know how actual gunslingers spoke, dressed, acted, etc.: thus, what we know of "cowboys" in modern popular culture comes from a literary source that couldn't have been more clueless about the realities of western American culture. Hell, they even got the name wrong, for as already mentioned, "cowboys" were generally people who worked a hellish job that saw them fighting snakes, thunderstorms, and stubborn cows, not outlaws.

Now, to your question about some of the familiar western tropes, I can shed a little light on some of that. For starters, saloons varied wildly from region to region, and even within the same town. In a mining camp, a saloon might just be two barrels with a board over it that sold whiskey by the "pull" (shot). In other places, it might have been a grand establishment with a mirror (a big deal, and expensive), piano, gambling areas, and prostitute rooms. These wouldn't have been as common, but they did exist. The norm was probably somewhere between these two extremes, but again, depending on where you were and what the clientele was like, it really depended on the place and people.

As far as duels at high noon: this is almost entirely a fiction. Duels did happen from time to time, and about the closest anyone came to the classic duel in the middle of the road at high noon was a pistol duel between Wild Bill Hickok and a guy named Davis Tutt in 1865. Like the gunfight at the O.K. Corral, it was legendary, however, and spawned a myth about this kind of showdown that endured. (So like a lot of things in history, it grew out of a small, real event and took on a life of its own). For the most part, shootings were cowardly affairs that rarely followed any script, rhyme, or reason.

This concept of "cowboy" as an archetype really did grow out of the Dime Novel history I explained above. For modern audiences, what we perceive as a "cowboy" would have been called a "Shootist" at the time. This was a person who made it their business to be skilled with firearms, and practiced a lot to hone their craft. This was an expensive proposition (ammo wasn't cheap, and to get good, you needed to go through a lot of it). There were people who lent out their services in this regard (as hired guns), and WERE extremely dangerous (look up Tom Horn for an example). They were not nearly as prevalent in western culture as the movies would have you believe, however, and most didn't live a long or prosperous life.

This is a kind of quick and dirty explanation or some of your questions, but I'd be happy to respond to any others you might have on the subject. For sources, check out Michael Denning's 'Mechanic Accents' (a great read on Dime Novels and the origins of the cowboy archetype) and Richard Slotkin's 'Gunfighter Nation' which goes into great detail about the birth of "cowboy" pop-culture from Dime Novels to radio, T.V. to film.