Texture2D Power of 2

I have following questions regarding texture created in graphics memory.

For example, my terrain image size if 2035x749 pixels.

1. What size of texture is created? Either same size or 2048x1024.

2. If I create multiple terrains sprite using same texture then multiple texture memory allocated or not?

3. Also if I am using any 3d objects then what scenario get change?

I need only suggestions in this. Only concept become enough for me.