I am going to avoid commenting on mechanics, as it appears that you are playing 5e and I'm not personally too familiar with that game system.

As far as the physical appearance of your dark-kin, that is largely up to you. If you describe your character as having scales, or thick quills, or rubbery hide, or thick skin, it doesn't really matter so long as you use only the mechanics described in the rulebook. There are a large variety of infernals which your character could have potentially inherited that trait from, so feel free to be creative.

Generally speaking, however, the more infernal traits your character has, the more obvious it will be that he/she is infernal. I'm not sure whether it is converted for 5e already, but there is a talent in the ARPG which allows dark-kin to unlock more of their infernal heritage, which has benefits and potential penalties.

Feel free to be creative in how you describe your character, so long as you follow the rules listed in the book.

Hope this helps!

I'll echo that.

In the old campaign my Dark kin had no shadow and vibrant green eyes. No claws, no horns, no thick infernal hide.

I know that having more demonic appearance attracts more attention, but do living mods really right in possible encounters just because you are more odd looking?

Well considering those features I think what I have in mind is..
7 foot tall, all sinew and muscle, almost to thin, wearing a worn and clumsily patched but still maintained Milandisian Noblemen outfit. Shoulder pads or something from his legion? Or a cape with their symbol on it? Horns that sprout from the center of his forehead and point up and back, the front of the horns have small spikes. Skin is a light earthy brown and hair ice blue. Eyes like a goat with gold irises.

Or is that to much? lol. based on some of the pictures i've seen, it seems light.

This is typically left up to your Chronicler (GM). You need to go talk to some backwater villagers for information? Guess what, they run away screaming at the sight of the tall armed & armoured infernal warrior coming into town...or at minimum, decide not to be helpful.

I have seen it written into modules where the Tir Betoqui dwarves will attack dark-kin, so there is the possibility of unexpected combats. Keep in mind that Infernals are a terrifying scourge on Onara, so dark-kin are going to often be lumped in with that lot, at least until they prove they are different. NPCs who have never met you will often be frightened/standoffish.

If you are from a legion, the character is most likely from Coryan. It is very unlikely that a Coryani legionnaire would be wearing the clothing of a Milandisian noble...especially considering that Coryan and Milandir have gone to war in the past.

I would normally expect a legionnaire to have a tattoo on his shoulder or chest with the symbol of his legion, and then possibly legionnaire's armour (lorica of some sort). Otherwise your description sounds fine to me.

Second question is.

He has 1 level of barbarian, and now 2 levels of fighter also. I'm caught between Protection, Duelist and Pugilist.

I really want Duelist, but i feel my characters Massive Horns count as wielding a weapon, making duelist unusable.

Protection is a obvious fall back if I've no other options. I am already using a Shield.

Pugilist because it would just be another attack and after a charge it could drop the enemy.

Id be willing to explore other ideas for my weapon load out, but I feel i'm getting the best of what there is.

Warhammer, Longsword, Javelins, Gladius, Cestus, Horns. Primarily I use the Warhammer and Horns.

I don't think Duellist would be cancelled by your horns - they specifically made Unarmed not a weapon & it works with shields even though they are improvised weapons, up to DM though. Protection is fine if very boring.

Pugilist does not work with "charging" as the Horn attack & Unarmed attack both use your bonus action.

Hmm can I get an official ruling from somebody on the staff? In relation to the horns counting as a wielded weapon? I'd like to be able to show proof if questioned at the table.

I'm not anyone official, but due to how Dueling is worded, Horns do not count as a wielded weapon for purposes of that fighting style -

(pg. 72 5e PHB) "Dueling - When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon."

That being said, a different case for Claws could be presentable (not 100% sure here though).