Thunderbird does not have check boxes as you describe, so I assume you have an addon installed that provides them.

Thunderbird has no preview pane. reading a mail is reading a mail, be it in a window, tab or pane.

Right-click any column button, or click the icon at the end of the buttons, and enable the Select Messages column (see picture). Close the Message Pane (F8) to select messages without opening them,