It does not mean you are out of the wood, because you have to work your way backwards. On the other hand, the biggest problem I see in fantasy is writers who start with the religious practices they know, and slap the religion they want on top of them. It's not the religion that's the problem. It's that the foundations are all wrong.
The big one I see is treating the worship of individual gods as being like belonging to a different Protestant sect. Not likely. You'd have institutions like Rome's pontifex maximus, who was in charge of seeing that all the gods were kept placating with appropriate rites and sacrifices, and who needed a wife, and children -- foster children if need be -- because some rites had to be performed by women, and some by children. And random people would worship every one of the gods relevant to his situation. (Saint Augustine described a stock joke of the Roman comedy: the total fool, who would ask Bacchus for water and nymphs for wine, when everyone knew it was the other way round.) Even a dedicated priest of one god will join in the festivities for other gods. Eating the sacrificial meat for instance -- Pythogereans were vegetarians, but they would eat sacrificial meat because joining in was that important. Someone who worshipped only one god was a dangerous lunatic.
To be sure, there were differences about which gods were important enough to be worshipped. The Spartans had no cults for Demeter and Dionysus -- agricultural, whether grain or vine, was helot business. The Romans had the Capitoline Triad -- Jupiter, Juno and Minerva -- and the Aventine Triad -- Ceres, Liber (also identified with Bacchus), and Libera (also identified with Proserpina) -- which are also called the patrician triad and the plebian triad because of their affinities.
But, in the midst of this welter, note that while certain positions in Greek cities and Rome were later called "knights" in translation, it generally revolved about their being mounted. The code was that of the city and the city gods, not chivalry. You might get something like it in the forms of chivalry that emphasized the knight's loyalty to his lord rather than his being the sworn defender of justice and the innocent, or the lover of a beautiful, highborn lady. But it would be different even so. And if you want the sworn defender, you probably need a religion that has some degree of monotheism and dedication to higher purposes. (Greco-Roman paganism has moments like that, like the priestess Aristotle cited, who told her son to avoid politics on the grounds that if he told the truth, men would hate him, and if he lied, the gods would hate him, but only moments.)
Similarly with monks and nuns. It is not a coincidence that all the world religions with monasticism ascribe their origins to a teacher. The sort of religion that is so melded with daily life as to be not noticable as religion until you contrast it with somebody else's religion does not produce an ascetic bent. Rituals of mortification for sin or pollution, yes, but those are intermittant. Even among the Greeks, the sharp ascetic strain comes from the philosophers, who are often effectively monotheistic and strongly against the sort of interwoven with life religion about them.
So if you want a Crystal Dragon Jesus and to be convincing, you want to make your Crystal Dragon rather Jesus-like in enough ways to justify the religion having the practices you want. Some variation is possible of course -- as with the monks. And putting knights in another context would require somewhat more world-building, seeing as Buddhism's pacifist roots prevented it from developing a warrior ideal. You occasionally get something like it with the ronin, but then, you have a knight errant, not, perhaps, an order of knights. Depends on what the story needs what you need to build.