Time Machine will back up the iTunes Media Folder, which stores all of your music and video.....and it will also back up the iPhoto Library used with iPhoto.
Time Machine does not backup the entire libraries each time that it runs. Time Machine backs up the entire contents of your Mac on the first "master" backup. Once that is done, Time Machine only backs up the changes that have occurred on your Mac since the last backup.
So, if you have made any changes to the iTunes Media Folder or iPhoto Library since the last backup, Time Machine will pick up the change and back that up on the next pass when Time Machine runs.
Best to ask your question about Photostream in the iPhoto support area. My understanding is that images are normally stored in iCloud, but if you have downloaded images permanently to your Mac, they are stored in the iPhoto Library, which will be backed up.