Just searching the forum for "Thorns" gives over a hundred posts, and while most of them aren't relevant, it doesn't take long to skim them and find some of your information. There's even an entire thread regarding the
Inquisitor PaladinFor the questions you asked:
- Most thorns gear doesn't have high requirements, so you can go all-vita if you want (doesn't really matter though, unless you routinely survive battles with less than 1k life).
- Late game gear should emphasize absorbs and Amp curse, so Blackhorns hat, Hellmouth guants, Glassglare armor, Stormwalk or Wartrav boots, Atma ammy, etc. If you feel like micromanaging your absorbs then I'm sure you could get a bit more thorns% by swapping out absorbs in certain areas.
- Thorns only does damage based on how much life you lost, so dr%, dr, EShield, and BoneArmor will all reduce your flagellatory attack.
To quickly restate some of the stuff said in the past:
1) Barbs make decent Thorns builds because of:
1.1) High life skills
1.2) Taunt skill to cause creatures to attack you
1.3) Berzerk skill to reduce defence to zero
1.4) FindItem skill to get more pots (Champs are awsome)
1.5) Dual-wield SuicideBranch for 6000% thorns at lvl 45, and they can use Lacerator for a decent source of Amp while keeping 1500% thorns.
1.6) No pets (they'd just prevent monsters from attacking you)
2) The build isn't viable in Hell, since the global phys res of creatures is very hard for the build to overcome (Amp helps, but it's still nothing great). Another problem is the emphasis on Absorbs to keep you alive. Almost everything you wear to improve your absorbs or give you Amp reduces your thorns% output. In the end you end up a very durable but fairly ineffective Cheerleader. Without the Absorbs, you die too fast to elemental damage to kill things via their physical damage.
3) The build does significantly poorer in multiplayer, since fewer creatures attack you, and their life increases enough that they no longer kill themselves efficiently (There's a point where healing pots just can't keep up anymore). This reduces you to a BO and FindItem character, which is why I refer to my barb as a Cheerleader (two SBranches even look kinda like batons). That's actually still pretty great party support, but it's hard to get more boring than that.
4) The build rocks some bosses like Tobial (you have to back off on the killing blow or you kill the portal), Dury, Mephy, etc (Any boss that likes to attack a lot)
As a last point that I don't think I've mentioned before, I find that Thorns barbs are pretty great as a gold-find character. Running NM Leoric is quite fast (Amp him + he Amps you = he KOs himself in about 3-5 attacks), and it's not impossible for him to drop almost 1M gold per pile when you hork him with a couple GlitteringSun swords. My thorns barb used a few Wirt jewels in his gear for kicks, so his typical non-switch gf/mf was still around 400% I think