I haven't figured out the logic or have recognized a pattern as to how Visualize scales texture maps. So I can't offer any insight on that part.
For number 3, I can offer a tip for a faster workflow to apply appearances to multiple parts. Shift + Left click on an appearance that you want to apply to multiple parts. Then Shift + right click on each part you want the appearance on. That's the best tip I have for that one.
Regarding number 5, seeing the repeating pattern of a texture map is an issue with the map, not the software. The only way around it is to find better texture maps (a hit and miss proposition if you're searching the web for some), or make your own seamless maps that have less recognizable aspects to them when they are tiled. To illustrate what I mean, take wood grain for example. If you have a knot in the wood in the texture map, you will easily see the knot repeated and have a seriously unrealistic look to the appearance when the map is tiled. The knot will stick out like a sore thumb.
I've made some stainless steel materials for download if someone's working on vessel productions.
\Documents\SOLIDWORKS Visualize Content\Appearances\
I have another question, is it possible to save/convert visualize appearance to solidworks appearance?
Will future solidworks versions be able to use visualize appearances?