I would immediately suggest giving all but two of the duchy titles away to vassals, and definitely choose counts who own land within the de jure territory of the duchy you're giving away. Other than that, again if you don't own the counties themselves, you're only removing one person getting a 'cut' of the tax revenue and levies from the counties, but I would consider this not worth the -10 relations penalty (per duchy above two) that you're taking with all of your vassals.

All of the counties within this duchy get a bonus to levy size. Basically, the duchy you really want to hold is the duchy that contains your capital. The advantage of holding the duchies yourself is quite minor if you don't actually control the counties within the duchy yourself. As such, Brittany will never assimilate into Ireland, but, should you form Britannia and become an Emperor, after 100 years the Kingdom of Brittany would drift into being de jure a part of Britannia. There is a concept of 'de jure drift' which causes titles to 'assimilate' into others after they have been controlled for 100 years, but this only happens with a lower tier title drifting into a higher tier title. Outside of getting easy claims, the only time I'd create a kingdom is if I need to to form an Empire. You get a bit of extra prestige from holding the title, but the discontent it creates often isn't worth the trouble. Creating a kingdom 'just to have it' though when all the territory is already controlled has more cons than pros. Creating a kingdom is a good way to get claims, so if you needed the claims to take the territory in Brittany, then it could be a reasonable decision. Note that this is also true of counts within the de jure territory of the duchies that you hold.ДЄs for whether or not you should have created Brittany, it really kind of depends. Ambitious dukes will get a further -50, since you posses something they desire. While holding those kingdom titles, any Dukes within the de jure territory of those kingdoms (except for those with the 'content' trait) will get a -20 relations modifier for 'Desires the Kingdom of x'. The second disadvantage is that it creates more discontent in your realm. However, you can also have problems if, for instance, Ireland is on primogeniture succession and Brittany is on, say, Elective and the electors aren't voting for your eldest son. The obvious problematic scenario is being on Gavelkind succession, which splits up your highest tier titles automatically. You'll want to make sure that all of your kingdom titles have their succession laws set up in such a way that you can insure that on your death all of them are going to your heir. The first disadvantage of having multiple highest tier titles (in your case, multiple kingdoms) is that it complicates succession. Should I not have created the Kingdom Title of Brittany? Is there any disadvantage to holding multiple kingdom titles? Will the kingdom of Brittany ever assimilate into the kingdom of Ireland now the title of king of Brittany has been created?ДЄlso what are the benefits and disadvantages of holding so many Duchy titles? Should I have tried to not create them in the first place and should I have destroyed the Titles as I conquered them? Or should I give them up to my vassals?

Then I will have 3 kingdom Titles and Numerous Duchy Titles. I created various Duchies while expanding in Ireland and then went on to I create the Kingdom of Ireland itself, and through successful marriages I have inherited the kingdom of Brittany (The title of which I created as soon I could) and I am set to inherit The kingdom of Scotland as well through my Heir. I've only concentrated on not exceeding my demesne limit. As such I've been creating titles and keeping them to myself. I've been playing a game a Munster and progressed from 1066 to 1128.Дuring this time I was not aware of the Duchy limit of 2 and the corresponding penalties of holding more than 2 Duchies can incur.

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