You can only view photo stream photos on an iOS device or computer that is signed into your account with my photo stream enabled; you can't view them on icloud.com.
Music is not synced with iCloud. You can download music previously purchased from the iTunes store from iCloud but that is "iTunes in the Cloud", which doesn't use your personal iCoud account (and in fact doesn't even require an iCloud account). It is merely redownloaded from the iTuens store.
You can view all your data from within th apps on your devices that are syncig data with iCloud (calendars, contacts, notes, reminders, etc.) What you see on your device is the same data that is in iCloud. You can't view your backups anywere. You can only see that you have a backup in iCloud (by going to Settings>iCloud>Storage & Backup>Manage Storage); you can't see view any of the data in the backup, you can only restore it to your device if you need to.