I work in Photoshop CC & Illustrator CC with a Wacom tablet. I am new to the gaming industry.
I want to create hi-resolution backgrounds and 2d game art/graphics to sell on Asset store and use in a future 2d game.
In Photoshop is it safe to create a 1920 x 1080 document for use in Unity as a 2d backround?
Will it be possible to use painterly style 2d background graphics at this size safely? Exported as png?
Is Unity compatible with Illustrator’s vector graphics?
Okay. In the Unity Space shooter tut Pt. 4, from 2:14 secs.
https://unity3d.com/learn/tutorials/projects/space-shooter/adding-a-background
They used a space background, that was 1024x2048.
Okay, read this interesting info, on creating assets.
Scroll down to the part called textures.
https://docs.unity3d.com/Manual/HOWTO-ArtAssetBestPracticeGuide.html
In it, they say to make images, by the power of 2.
They also mention, that 2048x2048 and even 4096x4096 can be used.
But 2048x2048 might be better, with most graphics cards.
So yeah, you can make hi res backgrounds, for games made in unity.
Check the info above. 
Thanks BrandyStarbrite! 