- You can't craft fine clothing, because clothing is crafted using the Common skill which has a fixed skill rating that's not sufficient to produce fine result.
- I have to correct marginoferror regarding javelins: You can indeed craft fine ones, but to do that you have to buy fine staves for your input material, as you can't make better than decent ones yourself, because the starting material is for staves is always decent, and the result quality can't exceed that.
- I'd expect the protective value of leather to follow that of the corresponding hide (apart from the cold protection, of course), but haven't got any data to back that up.
When crafting, input material can either influence the quality of the output, or explicitly be exempted from doing that, causing the result to instead be based on the other input materials (and other factors, such as tool impact, skill, penalties, etc). You'd have to look at each recipe to determine which input affects the result.