play any song. now goto "File>New Playlist". now you can't see your previous playlist - clicking the bar at the bottom will take you back to the now playing track/playlist.
you can use the "Playlists" node on the "Library" tab or on the menu use "View>Playlist manager" to manage multiple playlists.
customising the buttons on this layout is pretty much out of the question due to how heavily customised it is. using a default foobar layout, it's very easy to change your own buttons - but in this case it's not.
start>search
%appdata%\foobar2000
will bring up a folder with your config file in. it's named
foobar2000.cfg
this contains all foobar settings so you can back this up before experimenting with other settings. just note that changes are not saved to this file until foobar is closed.