You can learn what included in Object Desktop package by visiting this page : https://www.stardock.com/products/odnt/
No, you do not need to design your own Curtains or Windowblinds style or you own Icons package to use those customize application like Curtains, Windowblinds, CursorFX, IconPackager, Deskscape, SoundPackager, Start10.
You can download via Wincustomize.com for those styles and Icons packages. Most of them are free. Some are Masters premium styles and packs which are paid download.
Stardock Community Assistant.