What *kind* of visualizer are you building?
Final Cut will not accept new audio tracks in a template used to create a visualizer. You can save your visualizer as a template, but the audio response will be "burned in".
How Motion works is: it takes the audio track and creates keyframes for animations. Once that task is completed, you can basically delete the audio clip from your Motion project — the animations will remain.
You can save your individual track visualizers as FCP templates — it's a much more memory efficient way of saving and using the visualizer in Final Cut compared to exporting the visualizer as a ProRes 4444 video (assuming you want the graphics overlaying other media).
You *can* publish parameters for appearance, color, scale, position etc., which may help streamline your "process" and/or make it easier to change the appearance to fit your video. You will most likely have to readjust the Project Length for each music track (or create of a fixed "maximum length" that you're sure all the music tracks you use will fit.
However, you will always need to open the template in Motion, load in a new audio track and have Motion create the new set of keyframes for the (synchronized) animation.
I would recommend that if you decide to make your visualizer a template, that you name it <type of visualizer>-<music track>. You can Open in Motion any of them and Save As for the name change after changing the audio source.
A music visualizer is a little deep for a "noob" but don't let that discourage you. Keep this thread going if you need more help along the way.