To your other question, the story is the same regardless of whatever class, race, or gender you play. The main difference will be in some dialogue options and NPC responses based on those things, but other than that, there is no significant change.
True, but with one important exception: the race and gender you pick controls which NPC you can complete a Romance with.
Female Elf has the most romance options -- I believe only Cassandra and Dorian are ruled out. Details here:
http://dragonage.wik...e_(Inquisition)
There is a point to creating more than one character (I believe what you meant by "account" and "file"). Actually there are three points.
1) There is a forced quest choice that denies you the other option.
So, to fully experience all the content, you have to play a minimum of two playthroughs. You could do it with one character, by reloading to a save before the forced choice, but why bother doing that? The forced choice happens very early, the equivalent of Act I in a three act play, so replaying the same character through the same content for Act II and Act III is boring (not to be confused with DA2, also trying not to spoil content in DAI). Why not create a new character and try something new?
2) Multiple playthroughs for different victory conditions/difficulty levels
For example, you might do your first playthrough on Casual and focus on story, skipping through most of the combat and crafting. Second playthrough, you might try Nightmare difficulty and focus more on crafting and combat, skipping through the story content you've already seen.
Then there are different victory conditions. I did one playthrough where I did no crafting on Nightmare. I did another where all I did was hunt dragons, I ignored the main quest starting from Act II on. I did another to try out a dwarf Artificer (current run), which I had never played before. And so on.
3) There are 3+2 classes and each class has 3 specializations, for a total of 15 specs
While it is true there are only 3 classes, the Rogue class has two weapon types, Archer and Dual Wield daggers, and Warrior has two weapons types, Weapon & Shield and Two-Handed, which are sufficiently different that they can be counted as two separate classes. Then each class has three specializations, although the same three specializations apply to both Archer and DW or W&S and 2H. Arguably you have 15 different specs.
You can have a maximum of 3 additional party members (4 total) for any given quest or exploration, but, you can swap party members between quests at camps. You can also respec characters fairly easily, though the main class (Mage, Rogue, Warrior) and the specialization can't be changed. Only the weapon type (e.g., convert an Archer to a DW Rogue) or the specific skill set can be changed.
So, assuming you acquire all the possible NPC companions, you could theoretically experience all 15 specs in a single playthrough, but it's impractical. You'll find that your character's class and specialization works best with only certain combinations of NPC supporters, so you'll settle on one or two party configurations for the entire game.
Which means that to really try all of the specs out, you'll do multiple playthroughs.