Is it possible to omit password from fast user switching and/or login screen?
Is it possible to be tweaked so that OS X won't ask for password when switching users? Or so that OS X won't ask for password in the login screen?


As long as they are not administrative users, yes. (Since you indicated you still want passwords for administrative tasks.)


  It is also essential that password is required for any remote login attempts — as they're in the default installation — be it SSH, SMB, VNC or the like.


In that case, you must only allow logins for administrative users.