Wow thank you :) for the quick answers.

I hope to create my own skin textures, because I am not certain in how far I have to credit the actual creator of a skin-texture even if I altered it. It's a bit tiresome to list all the creators of the packs/textures I use when showing my stuff at deviantart sigh

Selling my creations or edits of existing material is not an option as I merely use it for my private joy to create characters (for friends, who want to see their avatars in 3D) or give characters of my novel (I am a hobby writer, not commerical yet) some "visual appearance". But I dunno what happens as soon as I get one day a book published and want to use the characters I have created with bought, yet edited, material as base for illustrations.
The original creator of the texture usually has all rights reserved, I guess.

Will dig through the information as soon as I am at home :D Thank you again!