Official DA Comics & Novels suggested reading order?

The expanded universe starts with these two books.

The Stolen Throne
The Calling

These two novels precede DAO and pretty well have to be read in that order. However, the events of the novels are so old now that you could probably skip them and just read a synopsis on the Wiki.

After DAO and DA2, these three comics occur:

The Silent Grove
Those Who Speak
Until We Sleep

They deal with the lingering question of “What happened to King Maric, the father of Cailan and Alistair?” Note: they are set in a continuity where Alistair became King.

These three novels take place just prior to DAI. They can be read in any order.

Asunder
The Masked Empire
Last Flight

Asunder explores Cole’s backstory and The Masked Empire is about how the Orlesian Civil War started. Last Flight reveals how the griffons died out and contains plot elements that are potentially VERY IMPORTANT for the future, so out of these three, I'd definitely give it a look.

The comic Magekiller is set during DAI. However, it’s not that great; I’d either get the comic cheap or just read a synopsis off the Wiki.

Knight Errant takes place after the defeat of Corypheus. It’s quite good, and contains hints for the future. All five issues are out now, but I think there'll be a collected edition out in January or February.

If you only want to know about potential characters for DA4 then all you should read is Magekiller and then Knight Errant.

And I'd definitely read Asunder (Mage/Templar war explained) then Masked Empire (The Winter Palace Drama explained) then Last Flight (which actually overlaps the timeline of DAI, imo, as those wardens hearing the False Calling caused by teh Fear Demon are referenced.)

Reason being, the Mage Templar war started before the Orlesian Civil War. And none of us are sure when the False Calling began, so, "shortly before Cory blew up the Conclave" seems about right to say. So that tseems to be the time order in my mind.