Logan5579, you're right. Once the metals are alloyed, us garage metallurgists aren't going to separate them into their constituent elements. In liquid form, the atoms tend to disperse evenly throughout the mixture and in solid form, the impurities (like tin) substitute themselves in the matrix for atoms of the base material (lead).
As far as oxides, fluxing and skimming goes, the idea behind it all (as Fryxell discusses in his excellent guide) is to flux to draw the organic impurities out of the melt, then skim those impurities (as well as extra stuff like steel clips, etc.) from the surface of the melt. If you're using a bottom-pour furnace, then you shouldn't have to skim again. A layer of oxide will form on the surface which will protect the bulk of the liquid from further oxidation.
Beyond that, I'd just say refer to the online guides mentioned by the OP because they're some of the best information you'll find.
Oh, and I've found that the stick-on wheel weights aren't pure lead. They're definitely harder to load than store-bought balls, but not enough to fuss over.
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