There's some merit to the idea of starting a new character. The quests in the starting town are different, so feel free to make 2 new characters in the other towns if you want to watch their story arcs. In the meantime, you can also reacquaint yourselves with the basic controls.

Feel free to do the class and main scenario quests also. You won't have to grind any levels or gear for them, and it will teach you about the new mechanics involved. If you're in a dungeon, the best way is to explain that you are a legacy player and to ask them to treat you as a new player. You're already overgeared and have all the cross-class skills, so you're still better than a new player in that regard. Most will take it in stride.