I'll concede on the Picts. The qoute about Mac Alpin is from a nun who supposedly knew him, Da Ui Manna, but she was short lived, and accused him of some rather wild things. However, she did live among Picts at one point and called them Cruithe. I'm not so much basing my belief upon scholarship, but upon my trust in the people who dealt with them so much, namely Donan and Columba. Modern research can do a lot, but it isn't the same as standing in front of some one and noting their physicality. But I digress, as my sources are based out of period, and I'll concede that then.

As for Hibernia, there a few schools of thought. The earliest divisions are supposedly Leath Heremon, the north, and Leath Eber, the south. However, those are based upon oral tradition, and are the oldest possible divisions of Ireland by Celtic kings. However, their existence comes to serious question. Later, there were Leath Cuinn and Leath Mogha, again, there is no certainty they ever existed, but they are generally believed more than Heremon and Eber. However, those divisions also occured around 125 AD. Heremon and Eber would've been BC. However, the original kingdom names are possibly Cuinnacht (Connacht), in the north (as Ulster was quite possibly a sub-kingdom of Connacht at a time, and the kings of Ulster are believed to trace to subordinates of the king of Connacht), and the southern half would be Erainn, which was less of a kingdom name and more of a designation of the people who lived there (Erainn is the preamble to Aran). However, Cuinnacht is the same thing (Cuinn Men, which, whether Cuinn of a Hundred Battles lived or not, was the name of the people there). At this time, Laigin, Leinster, is part of Erainn, which will eventually become Munster.

The 'capitol' of Erainn would be fairly enigmatic. The various kings would change the position of it commonly, based on tribal ties, usually. There is a city on the west coast, from which modern day Galway is supposed to come, called Regia Alterior, but there was also a port on the west coast in the same place as modern day Wexford called Menapia. I recommend one of those for the city, and use the other for the port.