This is an odd thing to begin with. Jewish families always had fancy allegorical surnames like Silver Stone or Gold Mountain. And yet they ask us to believe that this gold merchant living in the city ghetto had the surname Farmer like 10s of thousands of German peasants.
Why?
The name Amschel may be a clue, because it is the same as the Dutch name Amstel which was a river that gave Amsterdam its name. Amstel comes from Germanic Ama-stelle meaning Water place or more precisely Current place. So if Amschel was destined by his parents to be a FARMER OF THE FLOW it may make more sense to have the name Amschel Bauer. Usury is, in effect, farming the money flow. And Gold trading is a form of usury since you always buy it at a lower price than you sell it for.
Is there any evidence that the family had that surname before Amschel? Or where he came from?