Slider Questions – Newbie

Hi, I am new to this.

1. For the slider on the front page, what size do the images we put in the slider need to be?

2. How do I add text to the image i put, would i Have to do that in photoshop first before i upload it or can i add text underneath using the “description” box?

3. Do any file types show up best?

4. Is there anyway to access the demo slider that comes with the template to modify and use those vs. uploading new images?

Thanks!