Thinking about returning and have some questions

[Enkidoh]

There's many different ways to level now - although you're still free to grind on FATEs if that's what you like. Some of the new methods for levelling are:

Duty Roulette (a dungeon is randomly selected from the ones you've unlocked and you get an exp and gil bonus for completion)
Dungeons have had the exp yielded by enemies increased considerably
Likewise, Guildhests have also had exp bonuses added as well
Challenge Log which is kind of similar to doing Achievements, only it resets once a week and yields exp and gil bonuses, amongst other things
Levequests have also had their exp boosted by a fair amount
From level 40ish, Beastmen 'daily' quests which you can undertake up to six a day which resets once a day as well

If you're wanting to level with friends, then dungeon roulette and guildhests would be the way to go.