My first game with CK3, about 900 hours on CK2, so I decided to try out with Petty-King Alfred of Wessex, listed as being hard.
Here he is as Alfred the Great, King of England in 902, gradually acquiring the missing bits of it.
Mercia lost, badly, to Jorvik and came back through a Peasant Revolt, got attacked again by Jorvik and Subreyjar and I realised that I had a much bigger army, with most of the Strategist line in Martial. So, by 897, I was able to take it over and create the kingdom.
First daughter was married to the Earl of Buchan, lost him in a Scottish war against Subreyjar, and is now the Basillissa of the Byzantine Empire. First son was married to Tegla Brycheiniog, was killed by a Viking, and she is now betrothed to the son of the Earl of Oxford and has a claim on Brycheiniog. Second son married a daughter of King Causantin II MacCinaed of Alba and was killed by another Viking. Third son is betrothed to another daughter of Causantin II MacCinaed and the second daughter is betrothed, matrilineal, to the son and heir of Infante Lope of Navarra, Duke of East Francia.
So, not to bad for a HARD start.