On a Mac, if you want a custom screensaver you'll need some way to install it other than System Preferences. I assume the same thing is true for PCs. It is pretty easy to share the files over a company network, but you'll have to talk to IT to figure out exactly how to load up custom screensavers. AE can produce the video but I don't know of any way you can a movie to the Library>Screensavers directory. You can put stills in there. Any custom screensavers I have ever purchased can be installed by double-clicking the file. I don't think you need special software on each machine, you just have to install them. A good 3rd party screensaver app should prepare a file that can ber installed.
I don't know much about the latest Windows backend because I don't ever go there. I wold just check the reviews and find some software that you like that may work.