Size of 2D sprites for non-pixel game

I was having trouble finding a direct answer to this question, and maybe that's because it's so simple. For a 2D game, I don't know what size to tell the artist to give me sprite sheets for environment, like tree pieces, mountain pieces, rocks, clutter, ect..
The pixels per unit for everything is 100. My character sprite sheet is 2048 compressed, on bilinear filter. Many of the animation sprites are around 200x200, or just under. This is going to be a PC release, so I have a little bit more room than something for mobile. Before this, I worked with 3D models and textures, so I am trying to optimize how I understand and use sprites.
Anyone that has any specific resources on bringing in assets for the background and world, or general answer to this question, I would appreciate your comments. I wanted to stress this is a non-pixelated looking world, so any direction towards a method in bringing-in a sprite sheet, their sizes, settings in the editor window and what I should communicate to the artist as she draws them. (i.e. Draw a 4096, put everything on one sheet no matter how large, break into sheets of this size, how to compress colors on sheets, ect.)

An early prelim. sample of the type of art is attached!

Thank you, everyone!

 

It is not technically necessary to put anything in sheets, since built-in Sprite Packer is able to repack everything to get best performance. Sometimes artists might prefer sheets anyway for color grading or project management purposes.

I don't have huge mileage with real life projects, so you might want to get second opinions, but personally I'd do the art of non-pixel game in maximum res possible. It is 10x easier to scale down than scale up.

 

0.01 Unity units = 32x32 pixels