You only have to add the xml’s & images that you are editing, the rest is filled in by the default theme.
The zip file has to be under 30MB, and you do have to include the “meta.xml” or it will not upload. The id is only for if you upload it to the WD server, which no one really does.
The .theme folder is only for the HUB, not the SMP. The HUB has an internal HDD and the themes are stored there for it. Themes on the SMP are stored in the flash and you can only upload one theme at a time (the default theme is hardcoded and can not be deleted).
By the way, if you are just trying to edit a theme, just open it up with your zip program (this works for WinZip). Then instead of extracting the files, editing them and re-zipping it, just click on the xml in the zip to open it, then edit it the way you want. Click “File/Save” then click back on your zip program. It should then ask you to Update the zip file, updated it then you can upload it the the SMP.
Same for images, just copy them directly to the zip.