What if you kept these first two ideas, and consider this. I love your idea as is, so please take it or leave it!

What if, after Egypt, he gets shipped to Britannia. He is assigned by Rome to a group who patrol around Hadrian's wall. It would be set up more like AC1 with a bit more travel between different cities. You'd have to repel 'barbarians from North of the wall' as well as assassinate and spy on Roman Templars who control the island and are busy exploring it for what treasures it could be hiding. The Assassins are more spread out here, and the Templars keep winning. So, your character brings together all of the Assassins from the area (knights of the round table style) and creates a Brotherhood. The Brotherhood either A) wins B) the Templars win, and as a result Eagle is sent to Rome to attack Roman Templars at their own stronghold.

Then the Roma edition comes in. Depending on the ending of the prior game, Eagle is really happy or sad, and he's deep undercover. He's just arrived and is trying to meet other Assassins, with no friends, and one million people living in Rome, he's at a disadvantage. So he basically starts with nothing, where you have him starting for that game, then it segues into your idea.