Richard, the appropriate size depends on what you are using it for. A picture placed in row formats behind page content will be larger than a picture in a slide show or gallery. As a general rule I resize all photos and pics to 1200 max width.

You are using the pro version so you have the opportunity to let WX5 resize to the appropriate size if you wish. Go to step 5, export project and select reduce the resolution of larger images.

When the iwzip is done, restart WX5 and select import to import your optimised project (this will NOT overwrite your existing project).