Heh, my German is very rough and I've only played in English so you're on your own on that one.
On the heir: Naturally you want to set your heir up with someone good, the eldest daughter of one of your fellow Irish counts(for your first run)
A. If his sons just so happen to die he(or she if a matrineal marriage) will become the consort when the current ruler dies. Now when your current character dies he will become count and his heir will be set inherit two counties.
B. In this game alliances are made with marriages.
On Ambition: Some like "have a son" will happen in time and give an increased chance. Others are more outright like become King of Ireland.
The bad part about playing a starter like Dublin is that it's absolutely fucking boring because you're just a single county. But it teaches you and shows you certain things in this game you have to be patient with. Once your father, the Count of Leinaster dies things will start swinging into motion.
You're not wrong on the hours of understanding though, I fumbled my first playthrough with Ireland. My first playthrough though was with Hungary, lol.
But don't worry after that you should have it down pat. I turned the Kingdom of Poland into the Wendish Empire with the crowns of Lithuania, Hungary, Bohemia, Finland, Pomerania, Bulgaria, Rus', Ruthenia, Norway, Sweden, England, The Papacy, and various duchies under that Imperial crown. At one point I became the Holy Roman Emperor too!