Backstab damage does not add to ranged damage at all right now, but I've heard through the rumor mill that there is a pending rule for them to add +1 to ranged weapons just like profs while still adding +2 from behind with melee attacks, but I don't know if that is going to pass for sure or not. Archery lets you shoot base 3 damage arrows, but if you go rogue you can take Alchemy and put weapon coatings on your arrows to either increase their damage or add a carrier to them, like Sleep or Nausea, and if the arrow does damage to their body and not just armor, they get poisoned.
If you are wanting to make a stealth archer-type, I would highly recommend looking at Scout class. If you take Weapon Proficiencies they add +1 to both archery and melee damage, and if the rule for Backstabs goes through, then you'd also be able to buy those to add +1 to your bow attacks, and be able to buy rogue skills such as Evade and Dodge, which take Backstabs as a pre-requisite.
If you've got a specific character-build type or at least skill set type that you want to try and make, you can also PM me here and I can give you some insite into which classes can make the most sense for your build costs to make it happen.