Au contraire, sir...
Your best bet is to have one drive dedicated to nothing but recording audio. In this instance it would be your external drive.
Your plug-in's should be installed on the same drive with your DAW. However, if you have a third drive, it is becoming customary to install the libraries (samples) for any virtual instruments on the third drive. But even then, your plug-in's themselves would still be installed on your system drive (C:\).