EE3 is the best mod about at the moment.. and this looks great.. but
You gotta keep the Scots as a playable nation (not a minor). I mean you can't underestimate their influence on England (yes, I'm scots - trying to be non-bias).
Right in the middle of that period you have the Battle of Largs in 1263 between King Hakonn and Alexander III. Had the Vikings won, the English were open to a mainland invasion from the North of a far superior force.
Not long after that you have Wallace (to a lesser extent than Braveheart suggests), Moray and Bruce and the Wars of Independance. You also have the first defeat of Heavy Cavalry in history (major militaristic milestone) and at certain points in that timeline, Scotland controlled a larger land mass of Britain than the English. Plus you also have the Auld Alliance with France and the establishment of the Stewart Dynasty around 1370 (which eventually resulted in the Union of the Crowns - the Scots King James VI became James 1 of England).
Peace with Scotland was absolutely vital in securing England as a nation. Without the security of a friendly Scotland, England would've been invaded by France from the North and South and thus cease to exist.
Not to mention what happens in the 200 years after that period. Scotland, Germany and England are the 3 central bases of the reformation throughout Europe. Granted not until the 1500's.. but relevant and shaped by the century preceding it. Until the reformation, Scotland was the key weak link in England becoming a major power.
IMO you can't have England without Scotland.