If your final case files are ready now, include links to them (via Dropbox or Google Drive) or upload them so that readers who accept can get started right away. Readers download them via links in the case reader request email; when a reader agrees to evaluate the paper, they also receive a link to complete the Final Case Evaluation form (CST-CASE).
As described in Appendix E of the STA Handbook, include one PDF of your final case paper, and a separate PDF containing photos of all sand trays.