Use the same email for all of them. You can use multiple accounts per authenticator and multi authenticators per account. Gonna test that one this week.

Leveling: I am using a combination of questing and instances. The Dungeon finder instances are +25% exp and good loot. There are several short instances that are scripted waves of mobs. Lots of fun and quick. I am usually waiting on the lockout timer on the short instances. So I will zone out of the instance into whatever dungeon it is attached to and start killing stuff till the timer is up.

I noticed I got rewarded for doing DF with a gift box that contains random loot. Gear, potions, housing items etc. The gear was level appropriate and Heirloom.

You will get good gear by questing. I have found some ground spawn collections that are not group collect and they are painful. Respawn times are not in line with groups doing the quests i.e. painful.