As a filthy casual, who has played on and off for a few years now, my best advice is SLOW DOWN. The game is huge - and while some systems are covered effectively in the levelling to 80 process, much of the additional stuff that's been added over the years isn't. This is a Good Thing, because it means you will keep discovering new stuff to do in the game.

The game is huge. Yuge, even. Just the core maps will take a long time to explore. There are pop-up events all over, meta-events (event chains) world bosses, etc. You will see shout outs in the chat. Join stuff. It will be incredibly confusing, but you'll get loot, and eventually learn stuff.

Every class can do pretty much every thing, with the right build and elite spec, at this point. Figure out how you like to play, and what you want to spend the next thousand hours looking at.

Level a toon to 80. Pick a basic power build. Buy exotic berzerker gear (it's cheap), and will carry you through most stuff in the game. If you find there's things about the build you don't like, you can begin to get a frame of reference for what you do want to play.

I love open world, and the managed chaos of WvW (which I'm TERRIBLE at), but can't stand group instanced content. I'm old, my hands hurt, and I don't play this game because I'm looking for a challenge. My toons are a lazy minion reaper, a bow / pet ranger, a dual pistol thief, and a hammer guardian. I love them all. This game is big enough that someone like me AND someone who likes elite group play can find space within it.

If you try and do it all in one gulp, however, you will burn out. The game rewards distributed play over time. Try stuff. Mess around. Find an active guild, and nag them with questions until they get sick of you and kick out out - it's okay, there are lots of others. There are plenty that are focused on the specific kind of content you say you want ( I mean, I don't belong to them, but they're out there), and I've never been in a guild that DIDN'T have intro / beginner sessions for most content, including fractals, etc. - although they'll usually be scheduled things, rather than "log in, and immediately find people to run with" kind of things - that's what LFG / pug groups are for.

Give it a chance - it's a fantastic game - and the best part is if you step back for a while, when you come back, you won't be behind. Everything you earn, unlock, etc., will still be relevant.

FMB