Newbie here, with a few questions!

[luxlunae]

"1.) have a level 90 on your MAIN account, and a level 15 (just an example) on the RAF/ secondary account and run duo dungeons. I think this is refered to as "Booster?""

This won't actually let you use your RAF triple levelling xp. In order to get RAF xp bonuses you have to be using two linked toons within four levels of each other.