How do you defeat Harold Godwinson in the William the Bastard campaign?

I got CK2 a week back during the Steam sales. I realised that most of the walkthroughs for William the Bastard are no longer valid as they were written back in 2012. As what Paul Marshall had said - the patches had altered the way the AI worked.

Two nights ago I finally managed to become King of England with William (after at many many replays). I think a fair amount of luck is involved plus the fact that I decided to splurge on a Mercenary company (I chose the Great Company for its heavy calavry. )

These are some of the actions I do to maximise my chance of winning.

1. When I first load up the game. I did my usual marriage and betrothal actions for alliances. Currently I am try to get an alliance with King of Norway by marrying William's half-brother (Odo) to his daughter. Then my sons to Denmark, Hungry or HRE. My experience was that immediately after I became King of England, HRE came after me instead of France and that ended my game rather quickly because there was no way I could win a war with HRE after all my troops were attrited.

2. Then I send my Spymaster to York immediately so that I can have a sense of the troop movement. Nine times out of ten, Harold wins against Norway without much losses. From there I keep track of Harold and have a sense when his troops woild arrive at Normandy. Usually it would take 2 months from the start of the game.

3. At the end of the first month, I would hire the merc called Great Company for the hvy calavry as I noticed that Harold does not bring them over to Normandy. What I do then is to wait until Harold lands and seige one of my county. Then I launch an immediate assult at him. The chances of winning is more than even. Thereafter I would keep going after Harold until his troops are depleted before he could flee back to England. This is important because if he gets back with more than 2k troops he is still a threat to you when you start your invasion. As yourself will also be too depleted.

4. At this point I take a look at my own troops. If I have more than 6k troops after dismissing my mercs, I continue with the game as it would give me sufficient troops to start sieging the minor counties in England. The reason I dismissed the mercs is because I found their costs unstainable and I became bankrupt after a few years if I am too slow in forcing the surrender. At this point I would say luck plays a large part. Because if you are lucky and net a few prisoners that gives 100 to 125 gold then keeping the mercs is not a problem.

I hope these opening moves help. Good Luck!