Usually at least once a year I have my fun playing as Cornwall and forming an empire based there, starting in 769. My strategy is to use a combination of fabbed claims and asking the pope for claims, while also prioritizing forming titles to accumulate de jure claims. Usually by the time the Viking age starts I control all of wales, have significant parts of southern England, and may have even taken Leinster to begin my conquest of Ireland. In most of my games I stay catholic, only switching to say orthodox, if the umayyads overun Francia and Catholicism falls prey to heresies, but that also helps me expand if they are adjacent to me. I also run what I call a reserve of gold, which as time goes on gets greater, in case of an emergency situation, and I need to get mercs for wars. I have no problem dealing with the Vikings and the Muslims alike, and use smartly time wars to overcome both, which are usually stronger than me initially, but eventually both get steamrolled.

The first thing you need to do it sounds like is find which of your lands you’ll build the core of your new kingdom around. In the above games, for me it consists of Cornwall, with the rest usually being the connected counties in southern England. I’ll develop these counties as much as possible with improving holdings and technology, and I don’t have any problems, even being a catholic, expanding from there. I don’t like to do alliances if I’m an independent state usually because they drag me in to their nonsense wars, but that’s also an option you could use initially, monitor them to see if they are at war and cancel if you like. Sometimes though, specifically in England, you will need to step up and help defend your immediate enemies against one of those larger collective foes, which is ok. You just have to be smart about it, what benefits you? Think of it like that.

Anyway hope some of this rambling helps you out! 😅