Okay I am going off a long shot here for the first part. Coveting also means envy, desire for. In this case I think Buffalo Bill feels envy for that which is his victim, he envies what she has, her skin. Remember he killed women of about a size 16 or 14 (I can’t remember that part.) He wants that, he envies that to finish his human skin suit or whatever he was trying to create. I never read the book though.
He had to basically starve them, but not so much that the skin would shrink. The lotion was to keep the skin soft and supple but refers to the Senator’s daughter as “It” so he could keep emotional attachments from forming. I think this is pretty typical of premeditative murder. The perpetrator needs to separate himself from the victim but at the same time has to have some sort of obession, especially in this manner.
As for the pictures in Fredrica’s room, they were not all that sexual, she was in her panties and suggests to me that she was “playing” around with a boy or boys. It could have been “Bill” but remember she sewed clothes and it wasn’t until Starling found the dress diamonds (for lack of a better term) when she put two and two together. Fredrica’s body, or one of the victims also had similar cuttings from her skin.
In the movie I don’t recall ever learning the exact relationship that Fredrica may have had with Jamie Gumm…I never read that book, maybe I should now.