Just want to know if FTP or SFTP connection to Slice is possible?
Or what would be a best way to move movie/tv show files from a another server (located outside of my home network) to slice.
It looks like Kodi supports ftp as a source:
but that may just be for steaming. I'm not sure if you can use it to download files and store them locally. It should be possible though.
Mo has made a "How to" video on adding sources here:
Slice has an underlying Linux. In worst case, you can set this up at your own (maybe with the help of a search engine). Same as for SMB/CIFS (the Microsoft Filesystem), TFTP, WebDAV, ..., whatever.