Tom,
Resizing images outside of Shozam before importing them into the program should save a lot of time in displaying the thumbnails in Step 2 and then in generating the gallery in Step 5. It will not make a difference in size of the generated gallery files or in the upload time in Step 6.
However, you may find it better to lower the image quality to 70-90% in Shozam. The difference between 90% and 100% is most likely not noticeable but the difference in file size can be quite large, requiring longer times to upload gallery as well as longer wait times for viewers to see the images.
Note that 100% does not mean that image is "left alone" and the compression from Photoshop is just passed along. Since Shozam resizes images, it does require the image to be re-saved and at that time to be recompressed. 100% quality (with so little compression) is somewhat an ineffective way of using a JPG file format.
You may create a test gallery with just a few images and try the various compression settings and see what is the best compromise between image quality and image size. It is likely to be 70-80%. However, if you find anything different, please post as it may be interesting to other Shozammers.