You do not have to give up Fvwm. I use i3, tiling (dynamic) window manager myself.
To mount USB drives and others, you can use a file manager that will do it for you, for example Thunar.
You can also use an independent tool called udiskie.
You probably have it in the repository. At least Debian has.
If not then you can download directly from GitHub:https://github.com/coldfix/udiskie
It is also a good place to familiarize yourself with the features, see screenshots.