hello, i dont know what kind of game do you like to do, but for your name i think that you like to do something like sims... well, you can get object for sims here:http://www.thesimsresource.com/downloads/browse/category/sims3-sets-objects/
i think that you can use this objects for your game... and there are a lot of webs with this type of material. But in general who develop a game with wintermute use her own pictures or drawings
Can I customize my characters?
you can model your characters, drawing in 2d, or modeling in 3d, and put your own character in your game. And you can do this with objects and all the images of your game.
i think that you need an illustrator, search him and you can do all you imagine...
about network game, no, wme not is an engine for network games, her main purpose its adventure games and dont implement network functions.
note:sorry for my bad english