One thing that's been mentioned is a ring that prevents the wearer from aging and presumably death. But there's no manifest that lists all these things. Many of them are going to be created as part of design experiences for dukes and monarchs so you won't know what these are anyway.

I imagine for the purpose of balance, a ring that prevents aging and subsequently death by aging, wouldn't prevent death by CDG after a certain age.

An Artifact is an object made by a human being, typically an item of cultural or historical interest. Where as a Relic is simply a an object surviving from an earlier time, especially one of historical or sentimental interest. So my view is a Artifact is more historical or from the cultural past and a Relic is something more mundane and more of a personal nature.

As far as locations early in the game, I would think both would be located scattered around the world in places not typically accessed. As the game progresses you probably can find some in stores, local auctions, or from an individual.

As far as Effects, no one really knows yet. I would think some would have some effects and some will not. Just remember that the effects can be positive or negative so finding one may not always be directly beneficial. Or if it is it may have a negative side to consider as well.

Artifacts are items that have been used to achieve something remarkable. They will give their bearer a passive bonus. Relics are ancient items that have magical abilities. In order to activate the ability, the bearer must realize that it is a relic and know what action to do to activate the ability.

https://chroniclesofelyria.gamepedia.com/Items