Preferred Game Object Sizes?

Hello all,

I have finished animating my character and exported it in high resolution 1340 x 1400 images.

Now it is time to scale them down and add them to sprite sheet.

My question is…

1: to what size should i scale them (preferred sizes for devices)?

2: should i create single sprite sheet for all devices or create multiple sizes sprite sheets for different devices?

Thank you!