You may get a mission or be tempted otherwise to take Bruges until you have secured the British Isles. Towards the middle of the game, it will be your primary troop factory.
Caen should be built up into a formidable castle. Lose that and you lose your foothold in France. It is a rebel held town and can be quite easily defended with a small garrison at that town and a bigger garrison at Caen. You should also look to take the town to the west of Caen, Rennes. If you’re going to use mercenaries, you’ll need to have money so start building up your economy in your four British towns. This slightly hamstrings you for troop selection against the Scots but use mercenaries if necessary. You want all your British Isles towns to be cities. Our mini-army should take York first if possible because the Scots will also be looking to take it.
Caen should be armed with a few extra bowmen for a defensive garrison until later. Gather together all available troops, leaving only small garrisons in London & Nottingham. It is very likely that missions at the start will lead towards you taking York & Caernarfon. Common sense alone dictates that eradicating the Scots is the key to the opening moves. England has an enviable starting position in that it can very easily have 7 secure & safe provinces very early in the game with a “beachhead” province in Caen.