Well why not a new thread for each.
For deadline , i think perhaps on two months ... but the challenge goal was a little like the 24hours games.
You make something tiny and a mini level.

Even for your speher game , once you control it , and have shaders, you just make one little level and that's it.
It's not a big finished game , but a little one with one level , minimum features, but polished.

You could have some low poly challenge also :
Keep the scene with level and characters low in polygons.

Well , we'll se on participation , number of people if we continue after the first one.

Yes some confirmed people here have already projects or stuff going on, challenges are most suited for people without a project in mind or beginners also to learn 3D game making.