For now I keep the default chunk size of 8 (you can change it anytime for yourself of course), because I noticed that a chunk size of 16 slows down the editing a little bit.
I don't have much further optimizations in mind. What I can imagine is automatically adding LOD groups to chunks, with the Culling level already set to a user defined value. Maybe it would even be possible to do some simplification of the chunk meshes for LOD 1, but I really don't know how, and it feels like a very extensive addition.
Also I was looking into texture arrays, but they have some restrictions (all textures need to be the same size, for example), and also I'm not confident they would actually help with performance that much. (They would help with greedy meshing though, I guess.)
In any case you should use occlusion culling, which Unity can do for you.