I am playing with the mod right now, and I would say the way you treat some things can be considered controversial if not outright inaccurate. The fact that vanilla CK3 invokes only Sasanian legacy in Iran, and doesn't go further in time, is actually historically accurate. Medieval Persians had no idea about Achaemenids: one of the main literary works of the period about Persian legacy, Shahnameh by Ferdowsi, doesn't mention Achaemenids at all, but he obviously knows of Sasanians. That's said, let's imagine they would like to learn about Achaemenids with resources which were available at the time: the only sources they could've used were the same available to European scholars until the 19th century, namely, works of Greek and Roman writers. If we go with that, then some basic facts are wrong: you give Stewardship experience for Cyrus trait, and Martial experience for Darius trait. This is exactly the opposite to what, e.g., reader of Herodotus would think about those kings, since Herodotus considered Cyrus a conqueror, and Darius an administrator. Specifically, Herodotus writes a lot about supposed reorganization and taxation reform Darius introduced. Modern scholars think this is inaccurate (some reforms had to be already in place during Cyrus' time), but Medieval reader wouldn't know that.
Then you have an event when you can get "Cyrus' coin" or "Cyrus' ledger written in Old Avestan" (yeah, "Old Avestan" is proper, not "old Avestan"). So reader of ancient writers would know that coins were again introduced by Darius, not Cyrus. They would know also that there was no face on these coins, but a representation of a Persian archer. Faces on coins appear only in late Achaemenid period and Hellenistic period, and on coins made by satraps and Hellenistic rulers. Modern scholars think these coins, those introduced by Darius that is, were not in circulation in the Near East, but were specifically made to pay for mercenaries and such in Asia Minor. So they were never in use in Persia proper, so couldn't be found there.
As for Old Avestan, this language was never used for any administrative records, moreover was never written down until Sasanian period (although some attempts were made in late Parthian period). Medieval Zoroastrians would know that, because this was part of their tradition that Avesta was passed down only orally until Sasanians. Readers of Greek writers would rather imagine that any administrative records were perhaps written in Aramaic, or they would have no idea at all.
Presently, we know that in early Persian empire administrative records were written in Elamite (in Elamite cuneiform script on clay tablets), while Aramaic was slowly replacing Elamite and other languages (like Akkadian in Babylonia) for such purposes over time. Texts from late Achaemenids and early Seleucid rulers are exclusively in Aramaic. Also, modern scholars date Old Avestan to around ~1000 BCE or earlier, during Achaemenids Young Avestan could have been in use in Eastern Iran, but that's a speculation, since we don't really know. Achaemenid inscriptions since Darius are in Old Persian, which is a different language (but this wasn't used for administrative records). All of that would be unknown for Medieval scholar though. Still, finding an Old Avestan ledger would be an impossibility since they never existed.
A selection of Amastris as a representative of Achaemenids is a curious one, since she is a very minor figure. I imagine you wanted to have a way for non-Iranian character to get Achaemenid legend. I wouldn't make such restrictive choices: you should be able to get Achaemenid legend if you complete traits and perks, and your capital is in Persian itermezzo area (since it's a bit larger than regular vanilla Persian empire) and in Anatolia, this is enough work in itself, no need to be of Iranian heritage. Virtually all inhabitants of pre-Seljuk Near East would have some ancestors in Achaemenid period, so no need to limit it only to Iranians. Iranian colonization during Achaemenid times encompassed the whole area of the empire, was especially numerous in Anatolia/Asia Minor for example, so their descendants would still live there (and I am sure their DNA is still present among people in Turkey, because DNA research constantly shows that numerous waves of conquers did not change much the DNA composition of the Middle East population).