One story, carried through three steps.
You do not learn a mnemonic for each item from zero. The picture you learn for a radical comes back in the kanji, and the kanji story comes back in the word.
Learn the shapes
Each radical is one picture that looks like its shape.
The shapes make the kanji
The kanji story uses only the radicals you know.
A samurai too proud to be seen throws a cover over his face and takes to the road on his own human legs, where the only work left is to sell.
The proud samurai hides his face under the cover and trudges the road crying 「ばい」, buy, buy, since the only work left to him is to sell (売).
The kanji makes the word
The same samurai comes back to give you the reading.
The sell kanji and the to sell word are exactly the same, so they mean the same thing.
Face hidden under his cover, the proud samurai walks the road with a stuffed kangaroo, calling ooh, Roo, 「うる」, at every gate, since all that is left is to sell (売る) it.
