I had the same .ds_store problem , I think you can’t turn off .ds_store file creation on El Capitan or Yosemite … I usually delete all .ds_store right before packing my files and uploading them .
About your second problem … Why do you have to hard code the embed code ? Why don’t you let your buyers copy and paste the embed code from soundcloud / youtube or whatever they want and paste it to a specific meta field instead ? I’ve been doing that for years and I never had any problem with TF reviewers .
Good luck .