[quote]So, King Arthur existed, eh...? Or at least a couple Artorius fellows. Eire is still a bunch of warring clans struggling with Viking raiders, right? Or is it actually a unified place in this timeline?[/quote]

Magnus Artorius is whom most refer to as King Arthur, yes. Eire is a loose kingdom divided between petty lords and lands taken by Vikings.

[quote]Out of curiosity, what does C.E. represent (since it's taking the place of A.D.)?
[/quote]

Common Era.

[quote]Are there Pagan pockets of worship in non-Pagan lands?[/quote]

Indeed, but the various local churches might be trying to suppress that.

[quote]Oh, and I'm supposing we'll be adventuring to a backdrop of the forces of Chaos rising up at about the time we start adventuring? So all the creatures from myth and lore start appearing before we start our travels?[/quote]

The effects of the rise of Chaos will become noticeable only some time after the campaign has started. For a while, it will be just rumors.