Is there a progression guide for London 2038?

I’ve just started to play the game a few days ago (never played HG:L or HG:G before) and so far followed the storyline questchain while doing most of the side quests as well. Now I’m in Act 5, so I will finish the story on normal (elite) soon, probably around lvl 30.

Is this the ideal way of progressing with a new character or are there more efficient methods?
How do the special areas ( I’ve learned that there are places called the Abyss and Stonehenge which are kind of outside of the story mode) relate in terms of difficulty, loot and xp rewards to “normal areas”?

In general, if you were to start a brand new account, how would you go about getting forward in the game?

I feel like I’m missing out on something but so far haven’t found any guide on the web that would tell in details where to go at what level (or ilvl).

If I was playing a new character I would do exactly as you have done so far, and then repeat the game on Nightmare Elite. You are much stronger once you reach NME but the enemies are more lethal and tougher once you reach Temple station the second time around. For me personally, this is when the game actually really begins, and everything before it is like an extended tutorial. When you reach Monument the difficulty ramps up even further and you will find that you need to grind out some levels in Stonehenge before moving on beyond Monument station. Once you reach St Paul’s you will need to go back to Stonehenge again and grind out some more levels and possibly upgrade your gear.