If I buy hosting and domain via S Drive, can I upload the created site via Adobe's Dreamweaver? The site is already created in DW. I want to be able to upload, update and maintain the site via the Dreamweaver FTP application.

Honestly, I don't know. S-drive has been created with the Coffeecup apps in mind, and I doubt that they support DW's FTP. You could test it by uploading from the page https://www.coffeecup.com/sdrive/dashboard/[some number]/site/. I don't use DW, so I don't know if you need to export the files first.
Other people in this forum may know more about this.