Okay, I have a tiny bit more energy today.
Some thoughts in no particular order. These are from running all of chapter 1 from start to finish, plus running 10 or so one shot scenarios over the years. This was using 5e for the campaign and 1e for some of the one shots, as well as using some of the 6e rules in a 5e game.
*The exact edition doesnt matter that much. The core game was always the same. The newest version does improve how passions work and I think is better in that sense. Buy that one unless you find one cheap.
*A lot of people on English forums will say to get the 4th edition because it has rules for magic and a bunch of non knight stuff. Ignore those. The more crap you add to the game, the faster you will end up playing something the game isn't really that well equipped to handle.
* Get the players buy in. You are playing knights. This is a campaign about being knights. You will not play the same character at the end of the game, as you did when you started.
If you have that one player who 100% needs to play something unique, this isn't the game for them.
* Later you can justify characters from all over Europe but for the starting characters, have them be from ye olde England. It is very easy to get a starting group where nobody has any attachment to the land and that will heavily scupper tthings if you want to play the Grand campaign.
* Passions are key to how the game works and should taken at absolute face value. Yes, your character can swoon in a depression or they can be so in love that they can slaughter 30 saxons without breaking a sweat.
* The game never quite understands its own rules for personality traits and the scenarios use them inconsistently. Hand out experience checks generously for roleplaying. I often had players make trait rolls to see how they felt abut something. They were free to go against that (after all, people second guess themselves) but often they took it to heart.
* Combat is fine. It has a decent bit of detail but its meant to be fast. Mounted knights vs Saxons on foot is a typical battle early on, because it lets the players experience combat before the odds get too serious.
You can die VERY quickly though. It never gets tactical. On the upside, its one of the few games where mounted combat is not a pain.
* The mass battle (in 5e) is either a pile of dice rolling that has nothing to do with the battle (rulebook) or an entire second game you play (the expansion book). You will have to figure out what to do here. I ended up improv'ing a bit using the encounter tables since all the battles in the grand campaign are predetermined anyways.
* You can mix in magic here and there. The game works best when its 75% knights and 25% strange stuff. Suddenly encountering a giant will be very meaningful when they are mostly dealing with other knights or saxons.
* Do not neglect "day in the life of" stuff. Give them quick sessions where they can interact with their families, talk to the people on the land, meet some travellers and so forth. Let them follow up on these people and have them grow as part of the story.
* The child birth rules will probably result in your character having no heirs and 7 dead wives. Theres suggestions online for how to modify things a bit (such as CON checks for the wife), otherwise theres a high chance you will NOT have replacement heirs in place when the original characters retire or die.
* If you play the grand campaign, there is a specific incident that happens at the end of chapter 1 which tends to get misunderstood as being intended to kill the party, but this is not how its supposed to work if you read it carefully (unlike some of the epic battles where that can definitely happen)
* if you run the campaign, read 5 years or so ahead. The book has a habit of introducing people it sort of assumes you already know and events can feel a bit disconnected if you dont tie them together.
I hope any of that helps.
I'm sure others on here have plenty experience GMing it too, but I am happy to answer questions.
