How should I have split up my Kingdom (Eire)?

Gonna be honest, didn't read the whole post. But one piece of advice I would offer is educate your heirs with high stewardship. I do it for almost every character because it increases your demsne limit along with some other benfits. The same goes for vassals, high stewardship is always good. Never give titles to people with the ambitious trait, because they rebel often. Search for courtiers with traits like gregarious (helps with cultural conversion/stewardship) or zealous (religious conversion) to help with keeping the realm stable and less likely to rebel. Also landing family is good, you should do that whenever you have to give up land and have unlanded family members as theyou are less likely to rebel.

Dukes are happiest when they have all of their de jure counts as vassals. You want to make sure that your personal counties are either in your personal duchies or in duchies which haven't been created. Then make sure you don't have as direct vasals any counts for which duchies exist. That's a -25 penalty for each.

My advice...

My Titles

lots of stuff...

I have a hated ruler right now with lots of armies at his fingertips so I figured now was a good time to revoke some titles, squash some more rebellions, and reorg the country.

This is the important bit. Revoke them all. Every. Single. One. You have zero count or above level vassals at the end of this. Revoking. Banishing, the works. You're mister Greedy Bags. Then we can reorganize the entire system at once, to our perfect liking.

How would you divide up the kingdom amongst your vassals?

As many low level vassals as possible, with Ireland you should be able to have all your vassals directly report to you, no dukes.

What traits are you looking to capture in your title holders?

Content, Gregarious, high stewardship.

What traits do you severely avoid?

None, but I manage any ambitious vassals closely. I wouldn't recommend getting any of them until after you have a handle on the game, and definitely don't try to work them into your plans.

Just make sure to manage your opposite traits (zealous/cynical, etc).

What are some hyper-optimal ways to break-up Eire amongst your vassals?

Everyone should report directly to you, and you want one coastal, count level mayor. He'll have a negative opinion modifier toward you, but he's going to give you a lot of money, and eventually you're going to grant him the duchy that he's in, so he can form a trade republic and boost your entire realms income significantly (although he will pay less direct taxes to you...).

I was torn between handing out duchy that I'd invested in early on, like Mide, that has a smaller size vs a duchy like Ulaidh which I'd invested nothing in but seemed stronger due to landmass and overall potential holdings.

Destroy them both. You want to hand out none.

Is it possible for me to find a happiness equilibrium as succession occurs?

Yeah, you'll have a slight negative opinion modifier but you'll probably pick one or two of those up along the way when you're older on the throne, too. You just work with them, apply a little (golden) grease to the squeaky wheels in order to prevent factions from firing and, in time, show the world your good graces.

Also, tech up. It helps.

Notice how the other Duchy holders in my Kingdom also own a County? I couldn't seem to find a way to give them JUST the Duchy. Is that intended?

Yes, dukes need land to be dukes.

By handing off the counties that should be under the duchy control of Connachta or Ulaidh I will gain favor but I want to maximize power in the King, what should I be considering?

Keep them all. Destroy the Duchies, you lose direct taxes when you create dukes, only do so in order to stay below your vassal limit.

Taxes:

A baron pays 10% of his gold to his count, who pays 10% of his gold to his duke, who pays 10% of his gold to his king, who pays 10% of his gold to his emperor.

Every holding of the same type has the potential to yield the same base tax income, so the more layers of taxation, the less tax you get. In fact, as an emperor you make almost nothing from the first few layers of taxation, and all of that is you have minimal, instead of zero, feudal taxation.

I'm also fairly new to the game but I feel my file with Eire has been largely successful.

So far I've unified Eire as the king, and completely taken Scotland and most of Wales. All of my direct vassals have positive opinions, and I have about 2000 gold on hand at all times.

What I did:

• First, never hand out land to family, especially non heir sons or brothers. Look for non related courtiers that aren't ambitious to make earls.

• I kept the duchies of Mide and Connachta for myself as well as the four counties that make them up.

• I made Laigan a merchant republic (give a county and then a duchy to a mayor).

• I made Gwynnedd in Wales a Prince-Archbishopric (give a county and duchy to a bishop).

• I also hold three counties in Scotland that I just didn't create the duchy for to fill out my demesne.

• I would give out the other duchies to earls with traits you like. Fewer direct vassals gets a little bit of a total tax decrease but they are much easier for a new player to opinion manage. Plus I make 32 gold per month as is which is enough for me.

This post was also very helpful for me getting started. Read the comment and his reply to himself

I hope this helps!

It's generally a bad idea to give titles to family members, as they will often have claims to your lands and each other's lands. It can be ok, as long as they're sufficiently distant to not have claims, but it's hard to tell who will inherit claims and who won't. Personally I just avoid landing relatives full stop.

Ideally you want vassals with no family, as upon their death the land will go back to you. To achieve this you spend piety or gold on the 'invite priest' and 'invite noble' options on the intrigue tab whenever you have spare land to give away. This prevents your vassals from inheriting from each other and becoming threats, and if any die before reproducing, you get to hand it out again and get happy vassals.

If you hover over the opinion of each vassal, you'll get a breakdown of what they feel as they do. A mistake I made a lot was not giving dukes control over their whole duchy. As an example, if you have a duke of meath, but the earl of Dublin is your direct vassal, he'll be pissed with you. To remedy, select 'transfer vassal' on the diplomacy screen, and transfer the earl of Dublin. He will now have his de jure duchy under control and will stop complaining.

The ideal is neat de jure borders, each duchy held by unrelated dukes who won't inherit each other's land and so will never become a threat. If one of your vassals does become too powerful, you can revoke a title without a general relations penalty if you catch him plotting.