Hi G O M
I'm not 100% sure what you are seeing 'THUNDERBIRD MAIL LOCAL FOLDER' but you can stop 'Welcome to Thunderbird' showing in the message pane by going to Tools > Options > General and untick the first bit, at the top, 'When Thunderbird starts ... '
If you can't see 'File - Edit - View etc' the press Alt to temporarily turn Menu Bar on, or right click at the very top of the window and click on 'Menu Bar' to have it showing permanently.
Events and Tasks can be turned on/off by clicking on 'Today Pane' at the bottom right of the window. Alternatively, you can click on the burger icon, upper right, and Events/Task pane is showing on my Tb window
If I'm understanding you correctly, you can adjust how much of the 'headers' you see by View > Headers > and click on 'Normal' or 'Compact'. I believe there is/are Addons regarding Headers if these controls are not what you wanted.
Also, if you click on the icon to the extreme right of Correspondents/Subject/Date etc, and click on Customise, you can move, remove, add various buttons.
Hope you find this to be of some help