Hi everyone.

I run a D&D 5E campaign set in Terrinoth, and one of the PCs is a dragon hybrid barbarian whose long term goal is to attain equality for his people. As part of his character arc (and also because the party needs a healer), he accepted my suggestion of multi-classing to a cleric, as a priest of Kellos. At the end of our last session, he was poisoned by a monster in a fight and came under the care of a Priest and a Knight of Kellos, and will be spending some time with them.

I want to play out the multi-classing in-game, instead of just awarding the character his new class abilities, so I would like to flesh out the theology of the Order of Kellos and the path to priesthood.

I imagine the path to priesthood will be in stages, with the character become first an Acolyte, then after undergoing the Ritual of Purification/Fire's Embrace become a full priest or knight?

The RoT book doesn't really have a lot for me to go on, so if you know of other sources of information, or have any ideas which you think are cool, do let me know.

Thanks in advance.