some textures, even though they are seamless, have a pattern you don't see until you put them together in the game.
That's true and I know this problem, but we actually have to decide whether we want interesting textures or absolutely no patterns.
I've already tested the textures in radiant. Some have patterns, others don't. As long as you don't use those "bad" textures for really big faces, it's not a problem.
The textures are all 512x512. That's not much, but it's 4 times bigger than the nexuiz textures (256x256). As long as you're texturizing small objects (i.e. a blender model or an object in a bsp map) you won't see a repetitive pattern.
Furthermore, as i said, there are quite a lot of textures without remarkable patterns.
Depending on the style of the Orxonox graphic we may need some more unrealistic textures
Yes, absolutely. You can easily modify those textures to make them look futuristic, but you always need an existing base and that's what I'm creating here. In addition, most of the nexuiz-textures I used for my spacestation weren't futuristic at all. They were just metal.