1 - If you want to use a skin on the a pure server, it will have to be on the server aswell. What happend in the quake world with version 1.31 there was a removal of that block only on skins. So people could have thier own custom clan skins on other pure servers.
Contact the admins of your favorite servers, and e-mail them the link to or the skin its self, I am sure most wont have a problem putting it up.
2 - I think Allow download will download only the required files. (IE the current custom map) However, there is a command to SET the required files, so if you wanted to force everyone to have your skin, put it in that list seperated by ;. (EG skins1.pk3;maul.pk3;mymap.pk3 )
You would want to make it very small as they will only download at a rate of something like 2 - 10 KB's per second.
Alex "Knight of Ni" Fex