I might be slightly off on the lvl numbers for those as I am going by memory which is never a trusty thing. However I did say lvl 14 for Emprise which is still within reason. If you would advise 14 or 15 I don't see a problem with that.
For what I mean by the last parts of Emprise and Emerald Graves it's this: Both of those maps have final sections that are pretty difficult to take on lower levels.
At Emprise you can manage the first section with even the fortress at lvl 15 but once you repair the bridge and head over to the section where the 3 dragons are you will encounter lvl 20 Red Templars and then the high dragons. This is pretty daunting at lvl 15, no? So I tend to wait until lvl 18, at least before I do that section.
In the Emerald Graves there is a section at the northern end of the map with lots of giants, higher level Templars, and a dragon as well as a lvl 20 rift. I tend to come back later in the game to do that section. Is my meaning clearer now?
Yes, But I'd still do Emerald Graves before Emprise. Certainly It would be the last fortress to capture out of the three, as it's the toughest by miles, and yet you put it directly after Skyhold.
Anyway Alexia, my personal rough order would be: (and I'd say that the stuff I've grouped together you can mix up a bit.)
Hinterlands (Val Royeaux as soon as you have 4 power to get Sera)
Storm Coast
Champions of the Just/In Hushed Whispers
Fallow Mire
In Your Heart Shall Burn
Crestwood
Western Approach
Emerald Graves (except the bit with the giants and the elven ruins and the Dragon)
Fade
Exalted Plains
Halamshiral Ball
Rest of Emerald Graves
Emprise du Leon up to the Bridge
Hissing Wastes (You might want to go there earlier and just find the dog shop to get good schematics before coming back to clear the region later)
Emprise du Leon after Bridge
Endgame