I just recently started making visualized music videos, but i dont own a youtube account and also dont plan starting a music channel, so i wonder if it is possible to create WMP Visualizations with AE?
Anything is possible with AE. The details will of course require a comprehensive understanding of techniques and effects as well as possibly requiring to buy commercial plug-ins.
If you're asking if something created in AE can be loaded into Windows Media Player as one of their visualization options, no. If you are asking if you can make a video in AE that can play along with a video in Windows Media Player, yes.