I use all 3+, but remove those icons I never use. FWIW I also use Context menues, so some of the relevant (book level) items my only be there.
The
Menu: (words only) Preferences, Help, Fetch News
Hoo boy! I have become a bit inconsistent
over time.
Main toolbar (no device) was supposed to be Basic Library (Add, Convert, send t...)
Main (device) dropped those that I would not need/use while a device was connected)
Secondary is
utility Plugins, things that may be used with or without a device connected