Heroes and other important parts of Celtic mythology are open to be played as reincarnations
... this should be Greek mythology, right? XD I only ask because Celtic/Celt is repeated several times in your FAQ (at least in the Old Souls section), and while I reckon it's just a typo I just want to clarify.

I would appreciate some examples of who would NOT be appropriate for an Old Soul character. For example, if they are considered too minor - IDK, Hippolytus, Troilus, Polyxena, etc.