Anya is a ghost merchant you can summon at any place and any time. She behaves as regular merchant, her inventory respawns every 2 days.
Spell is located just before Riverwood gate at a stone to the right (check out video). Anya has random alchemy ingredients, 100 of all ingots, leather, leather strips and 100 of all soul gems. But she will sell for 5x higher prices and buy for 5x less (base prices; can be modified by usual bartering perks and gear e.g. Blessing of Zenithar, bartering necklace, Cicero's clothes, thieves guild hood, etc.).
1/ Can I install / unistall mid game?
2/ Can the prices be cheaper? Can she buy stuff for regular prices?
No and no, she's designed to be help in later stages of the game, when your character has gear for bartering, high speech etc. So you do not have to run around from barter to barter buying stuff, when you have a lot of money and traveling to 10 merchants is just a chore. She is not designed to allow player to just buy 100 iron ingots and 100 leather strips over and over at the beginning of the game and level up smithing to 100 in 15 minutes after you've started the game. She's also not designed to be used as "offload useless stuff for profit" in the middle of a dungeon.
3/ Can you make her have all ingredients and 100 of them as with soul gems / smithing material?
No, even with 5x higher prices ingredients are very cheep and it would allow to level up alchemy very fast.
Unless someone changes that specific stone, mod should be compatible with anything. If you cannot find it, type:
help "ghost merchant"
into console and add the book with player.additem command
Reuploading anywhere is forbidden.
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