1. - I have a couple 1.4 characters going through the prides - If I go back to playing them, will I still get achievements? (ie if I haven't beat the game, go back and do so on a 1.4 character, will I unlock adventurer in 1.5?)
Don't export them, if you wanna keep going with them i recommend using the option of downloading the old engine you get when you try to load em
2. - Is there a way to make sure you get class specific artifacts? I currently have a doombringer, and every 2H tier 5 artifact I've found seems meant for sun paladins - is there any way to ensure or increase the chances of getting something like dethblyd?
Nope, just good old RNG
3. Speaking of artifacts, is there any general advice on which slots are best to buy from the merchant? My sun paladin went for a weapon, and got something that was not very good for him, so since then I've been trying gloves/boots as those seem to be more likely to be useful. Is that thinking correct?
Weapon is good if you don't have anything decent, other good options are utility slots like Lite, pickaxe, rings/amulets, gloves
4. Is the Vor Armory supposed to be so hard? My recent characters I've played (TW, oozemancer, sun paladin, doombringer) have been played on normal, and on all 4 I have only ever died to that. Going through the prides after has been cakewalk in comparison, as was dreadfall.
Vor armory is one of the hardest zones in the game, you're right about it.
5. Is there anywhere to get plain voratun amulets besides random drops? I've done the quest for the jeweler in the east, have some good tier 5 gems, but have never seen the plain tier 5 amulet.
They're pretty rare, you get 2 of them when you kill one of the postgame optional bosses
6. Are there any classes that use exotic weapons? I've seen some cool whips and tridents, but not til later, and only seen the exotic weapons unlock on escort rewards.
None, pretty much the only reason to go exotic weapons is if you plan to get Legacy of the Naloren prodigy, since you get one of the best weapons in the game with it
7. At what difficulty (if any) does it become necessary to drown NPCs and/or using an addon to choose escorts? I'm doing fine on normal without it, although getting correct escort rewards seems to have a huge (almost too big?) effect on the difficulty on some characters. Is this needed on nightmare, or not really until insane?
Insane and higher is the only ones you really need to care about it, since on normal/nightmare you won't really find mobs to drown on the towns (I guess you can now on nightmare, but it's not really needed)