Originally posted by ИΞCЯФБILΞ:

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Yes, there are mods that improve the general look of the game. I've also seen certain streamers change their model entirely to high-quality models with physics 'n' whatnot. I've personally not used either one, though, so I'm not certain how extensive it can be.

Yes, there is stability. Once you reach the iron age (about halfway through the current content), you can build rather impressive structures with the improved building materials. If that much stability is an issue, there are mods that can completely disable it.

And yes, you can build circular with enough space.