Heroes 5 – by Azmadon (Izmail).

Am I understanding correctly? The new class IDs simply allow you to add new classes, like Knight/Dark Lord, and then specify their "Available schools with probabilities," and configure the requirements for perks available to them in the "skills" section.
However, I don't quite understand how the "native faction" for these classes will be determined. Or am I simply forgetting about the existence and location of such a setting?
Another question: how does this work with the selection of heroes at the start and in the Tavern, including for old maps where, in theory, such heroes did not yet exist?
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*) Additionally, a question about "sets" of artifacts (including for these new classes) and the ability to customize them, although I don't rule out that I'm just forgetting where this is located.

Yes, the new class IDs allow me to create a priest for humans, a lord for dark elves, an alchemist for mages, and other classes that were in Heroes 3.
The class has settings for the probabilities of primary and secondary skills appearing. Racial skills are also secondary skills.
The native faction is specified in the file, just like for creatures (if I remember correctly).

This does not affect the selection of heroes. Heroes are separate game files, and maps also have a list of available heroes, so even if a new hero is created, the map needs to be introduced to it by adding the hero to the list of available heroes, or by disabling the list function so that all scenario heroes are available (with the exception of campaign heroes).

I don't know anything about artifact sets; I don't know how to do that. I would be happy if someone could teach me