This. The tutorial doesn't tell you everything - I don't think it tells you how to set rally points, which is a very important thing, and you're not told how succession works until you actually die - but it will teach you the very basics of acquiring territory and alliances. It also gives you a huge initial boost of money, prestige and holding improvements and you start as Catholic so you can get Pope gold too. I would recommend playing only until you fully form Ireland and then a bit longer to work out how to expand onto the mainland. Then, restart and try playing Murchad again from his normal start as an Insular Christian. You should still be able to form Ireland without too much trouble, but it will probably take most of Murchad's life to reach the point where your kingdom and permitted two Duchies are Tanist instead of 5-10 years.
I've got a reasonably decent handle on things but I am very confused by the tanistry succession.
When I first played from the 867 start I was doing really well, then I took the decision to make the Kingdom of Ireland tanist.
After that it all fell apart, I no longer inherited by primary duchy/county titles properly, and each new ruler I had would see me some place new, with factions popping up all the time.
On my next game I avoided tanist, but flipped to feudalism when I could, and then proceeded to go bankrupt. Apparently when flipping to Feudalism you need a good chunk of cash saved up to buy the upgrades for holdings as everything is reset building wise, and men-at-arms are now costing gold instead of prestige.
On my 3rd one I was killed off and the new king then did the tanist decision lol! I managed to get the kingdom title back but revoked the law to make it tanist.
What is the best way to use tanistry? do I need to add tanistry to my duchy title as well as the kingdom one? will that mean that the successive primary heirs always get both?
At least with the default law I was mostly able to gain some power back by keeping the duchy of Munster and revoking the two counties that split off under me every new succession with fabricated claims.