VST2 plugins you can keep where you like. You tell your hosts where they can find them. Still, different plugins may expect to find their content and other resources at a very specific location (see instructions and installers for your plugins).
In general, you’d keep VST3 plugins on Drive C, but you can put the content on other partitions/drive through the EW library manager.
VST3 plugins should always be in the same place on a Windows machine.
%SYSTEMDRIVE%\Program Files\Common Files\VST3
From VST3 you can also have subfolders if you like. I.E.
%SYSTEMDRIVE%\Program Files\Common Files\VST3\Steinberg
%SYSTEMDRIVE%\Program Files\Common Files\VST3\EW
%SYSTEMDRIVE%\Program Files\Common Files\VST3\Plogue
If you really want to host plugins on another partition/device you could use ntfs file system junctions (mklink /j) that ‘point’ to directories on some other partition. This can also work for content.
A filesystem junction is similar to a windows shortcut or a symbolic link in terms of function. In Junction form it’s done through the OS and Filesystem, so it’s invisible to apps themselves. As far as they know it’s all living at that junction path.
In the thread linked below I give an example on moving some stuff in ProgramData to a new drive/directory and then making a file-system junction that points to it from the original location.