Best resolution to create sprites at?

I'm writing my first game using Unity Free edition. This game will be developed for Windows 8.1/10 store/WP 8.1/10 as a Universal App.

The game will be a 2D sprite based volleyball game where the width of the volleyball field will be between 1 1/2 to 2 times the size of the screen(If a 10" screen the field will be between 15" to 20").

Because it's going to be a Microsoft Universal App the resolution could be 854×480, 1080p, 1920x1200(16:10), 2160x1440, 4k and many more resolutions.

If the game is played on a 16:10 screen I don't want to show black bars at all.

I'm using a Inkscape to create my sprites. I'm thinking the best approach would to create 2 sprites, one for 16:9 and one for 16:10 screens.

The approach of having two sprites for different aspect ratios, would that be the best approach? If so what resolutions would be best for each aspect ratio?

Thanks for everyone's help!