Unfortunately, there is no real compendium or documentation aside from tutorials/guides, communication between the community, and looking at how they did stuff in graph throughout the BPs.
For your other two questions:
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To add to the Main hud you can simply create a new widget that is a child of “PrimalUI” and add it to the viewport.
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I would refer to the “Lantern Pet” character BP (The parent of the bulbdog, featherlight, glowtail, and shinehorn) as these creatures rename those stats. you should be able to look at modified values to determine how they did it.