@rakuyo all objects should have applied scale or else it will cause unwanted errors for your customers when they want to edit the mesh. Non-overlapping UV simply means an object that has other objects UVs overlapping on it or the same mesh's UVs overlapping itself.UVs work differently depending on what the model is for, for example, if you are making a game asset the mesh should be scaled to 1, the UVs should well packed into one UV island and the mesh should not be loose from other parts. On the other hand, if you are making Arch viz models you can have multiple UV islands and maybe even overlapping UVs.Just head over to youtube and search "making a game-ready combat knife" and follow the complete procedure. If your models are not for games then you can just go ahead and model as you like but try to keep everything clean as much as possible.Hope this helps :)