No to both questions.
iCloud is not a permanent backup. You can redownload tracks if the tracks are still in the Store, and if the service is still offered by Apple, neither of which is guaranteed. You must keep a physical backup for that reason.
If you are using iTunes Match, then for matched songs you will get the artwork from the Store copy.
No, what you can re-download varies by country (music, films, tv shows can't be re-downloaded in all countries, and ringtones and audiobooks can't currently be re-downloaded in any country), and it also assumes that they will remain in the store - content providers occasionally remove their items. For music if you subscribe to iTunes match then you should be able to continue to re-download it, but that is only for music.
iCloud by country : http://support.apple.com/kb/HT5085
But, you should take and maintain your own backup of all of your purchases/downloads, rather that relying on them remaining in the store