Photoreflect question

Hi, I am going to start using Photoreflect to try and sell my sports photos.

My question is, before I upload my images I must-

1. Use the full image resolution?
2. Remove noise with Noise Ninja?
3. Apply sharpening?
4. other editing?

In general you should upload the finished image with all editing applied - for selling you probably want them to look their best.
It would also be a good idea to resize the image and ad a watermark of some kind.

When I upload the images it makes the gallery for me and it watermarks them.

Say somebody orders a 5x7 image, How would I work everything? do I leave it at 100% the entire time and never resize it down?

I need help I dont understand

A friend told me that I need to resize the image in photoshop to 5x7 at 300ppi. Is that what everyone else prints at, 300ppi? I just did a test print on my photosmart 7150 and it turned out beautiful, although I think it couldve used a bit more sharpening.