Determine Texture Size

If I have image of size 300 x 216 pixels which is non power of two. Below image represent my sprite setting for same image.

In above you see that I have created texture with 512 pixels size. After setting this question raised in my mind.

1. In graphical memory of device how much space occupied for same image?

2. Is it occupy 512 x 512 or original one?

3. What changes occur if I set larger one for that?

4. What is the difference in different format setting? Do we get any performance improvement?

I want some suggestion in above questions.