Upgrading of Items/crafting

yes, you can remove and upgrade to better. you can sell the old upgrades that you don't want or need anymore.

blank rune stones can be purchase from several merchants in the game.

you get the recipies/schematics from quests/missions and exploration, and a couple of recipies and rune stones {i think} as rewards for war room missions.

if a weapon already has a rune stone in it, it cannot be removed, but it can be replaced with another, which destroys the one already on it.

once you have the recipies, you'll need the elemental essences from kiiling diffrent fade rift creatures... spirit essence, fire essence, ice essence, lyrium essence, etc. All of which, iirc, have different levels of potency... i think there are 3 or 4 tiers for each. basic through pure.... pure being the best and most potent.

Ok now I know that I've collected some essences here and there don't remember what all they were and I just picked up I believe it was a fire rune schematic.  Now when we sell things does it sell our essences and crafting stuff like that there. Because from what I gather whil in game you can't sell things individually you have to sell from your valuables and sell all that is in there. and I don't want to lose things like my essenses yet I'm full in inventory.