Crusader Kings II

[Myth]

I have all the DLCs, I know that the tech system was different before (you could only favour which tech to get). I didn't know that Duchies mattered however. Inspired by these here posts, I started a game as the Jarl of Oppland (I think. The one who has modern day Denmark's capital). My life was all fun and games. First, the sons of Lodbrok asked who's face I would like to smash. I chose the Anglo-Saxon kingdom between Scotland and Wessex (so between Scotland and what appears to be London, Oxford, Winchester etc.) They died handily. Then I returned and told my neighbour to the east that I'm forming the Kindom of Denmark. It took some axe-to-the-face persuasion, but in the end he saw things my way.

Now a Kingdom, i raised Crown Authority to the paltry next-to-lowest state which I'm allowed and went to Ivar the Bonless's spineless son and informed him that from this day onward, Jorvik is part of the Kingdom of Denmark. A short debate involving axes and faces later, he too saw things my way.

Then I began playing "just the tip" with Wessex, chomping at their counties one at a time. They got the big idea of starting a holy war or two against me and failed miserably. Scotland also tried a holy war. Once.

Meanwhile i had some news shoved into my face, because I play CK2 on the highest speed setting usually, and normally have the political awareness of a potato. It turned out Sweden had formed, and for some reason we had East Fancia as a grey blob encompassing what I would call the height of the HRE's achievements - Capua to the south, my very borders to the north, a border with France and Lotharingia to the west (lotharingia was then promptly eaten by West Francia Grey Holly Roman Wannabee). To the east the Cumans and (surprise) my own Bulgarian Kingdom were having a hayday and the Basileos of the ERE was mainly preoccupied with not dying with his head impaled on a Bulgarian, Cuman or Arab spear. Strange, since someone reported that the ERE has a CB on everyone and anyone and it tends to blob like crazy with the Old Gods on.

So, anyway, It took some executins and encouragement to go join the Varangian guard to kill of all but one of my sons (pity the good one died young). I've been able to successfully emulate primageniture with Denmark this way. But I'm having trouble with the dukedoms of Jorvik and Pomerania, because thier leaders are always fighting someone within my borders. And that Pomeraninan bastard switched to Christianity and now half the time he is leading a faction to rebel against me. It also appears that I can't revoke a Ducal title without good reason.

I have two questions about this: do i absolutely have to form ducal titles? I can create 11 I think. I can also create the Kingdom of England and the Kingdom of Pomerania. Do I need to do so? How will Ducal titles benefit my technology? I've been stealing tech for 100 years already and I've slowly gotten pretty advanced.

I took a look at this whole "reforming the Norse faith" thing, but since I don't have the holy sites i can't do it yet. So I just subjugated Pomerania instead (hence the issues i mentioned above). And just as Sweden had fractured after an abysmal succession crisis and I eyed them and my good friend Fairhair's Ostlandet, suddenly, out of nowhere, East Francia started spamming Holy Wars at me. 20k stacks coming at me and that attrition bonus ain't what it used to be apparently. Now I have to huddle and wait for them in a province with rivers just to have a fighting chance. That, or spare 1000 gold in assassinations to get rid of their King. But I want to have a more permanent solution for them. Any suggestions? I'd take the usual subtle axe-to-the-face approach but they have more faces (and more axes) than myself, and they are mostly landlocked so I can't go all boats and scallywags on them.

Also, apparently I can call invasions and I didn't make use of this mechanic yet apart from the Lodbrok event. Would that help me do it?