I'm beginning to think that surviving the first few years is largely a matter of luck, even for a duke with several provinces.
Even if I start out relatively powerful, there is always someone more powerful nearby, who has a significant chance of annihilating me with me having no way to resist. Pledging allegiance to a king in the hope of protection does not always work, as even if they could protect you, there's no guarantee that the will...
Also, does the AI ever accept peace proposals when it is winning? I've tried offering it all my money, and the titles of any provinces it has claims on, and even when the value of this is far greater than the actual warscore, they still always refuse and keep fighting without mercy until they conquer all my lands.
Sometimes they will ...but if they are winning, there is no guarantee that you can buy them off first.
Thought you might want to spam them with offers of your whole treasury. You might get lucky that he will accept one of them.
When i play Nubia, half of North Africa will always declare war in the first few years. A war that I have no chances of winning. What I do then is let him come with his piece-meal regiments and beat one or two of them, and then offer my entire treasury. That usually works, and buys me peace with that realm for a few decades.
Which realms are you trying out as?? ... some are much more difficult than others.
As for counties to try, you could consider Lübeck. Mecklemburg pagans have a claim on them and their rulers are rivals, so you'll need to pledge to either Germany or Denmark to survive. I chose Denmark as it was easier to claim independence from them than a mighty Germany.
Pledging to them kept the pagans next door from declaring war for a few years. Enough time to build up my own forces (and Lübeck is quite a rick province) until I could take them on, with some help from Denmark.
If you are a vassal, the liege will ALWAYS declare war on the agressor, and should come to your defence. Well he might actually rather go for his own glory, than actually trying to keep your lands from falling.