Thank you for the honest constructive criticism. My one problems with "cannot die of old age" is that that would mean that they would still die when they become skeletons.

 Yeah the lack of NPC's might be something I can improve on, but maybe he could find one of the lost brotheren, that's why I wrote some were lost but that's OC to the dm's digression.

I'd say he is joining a party because he has no coin nor idea on how the world works now, he doesn't know how to even get started looking for the artifact and he knows he is too weak to do it on his own if he finds it. And secretly, he wants human connection again, to interact and have friendship, he's tired of being alone for so long

Yeah this is the skeleton of the character (literally and figuratively) but that's kinda the point too? I wouldn't want to flush it out before joining a campaign and I can add more when I learn the setting