You basically wanna do quests on the seasonal journey to get the ashes of something or another, and then put those into the XP boost. You do want to at least play the seasonal story until you get the pet thing, but it’s pretty good to just play it out.
You can get “Capstones” and “1-50” leveling for about 200fg on the trading forums, some people will offer it for less. But that’s the rushing route these days, some offer it to level 60 for more and in general that will be worth it if you don’t wanna play to earn the levels.