Photos:
iCloud: My Photo Stream FAQ
iCloud: Shared Photo Streams FAQ
Books:
iBooks, Kindle, and the Nook app do a fine job of sharing books across iOS devices, and in the case of the later two across most platforms. As long as you are using the same accounts on all devices/computers. With the exception of iBooks this has nothing to do with iCloud. Even then, it's not properly part of iCloud, it's just how iBooks works.
Bookmarks:
Safari's bookmarks can be synced via iCloud with other iOS devices and with OS X and Windows with the appropriate iCloud settings enabled.
iCloud: Troubleshooting iCloud Bookmarks and Reading List
Videos:
Well, if they came from the iTunes store, yes. Foggy on the details, since I almost never do this.
I'm not sure what is available with third party solutions. I mostly stream videos from Hulu or other apps.
In none of these cases is your iCloud storage limit affected. These are all extra services that come under Apple's iCloud/cloud service umbrella without having much impact on how your iCloud account is used. With the exception of Bookmarks the relevant settings are not even in the iCloud area. Check the settings for the apps themselves.