1. Get rid of page titles, page description, post titles… In your dashboard, go to APPEARANCE>MANTRA SETTINGS>GRAPHIC SETTINGS. This menu allows you to disable (and re-enable later) all these things (and more).
2. As Peredur previously stated, you can adjust your menu titles (and the pages they link to) … In your dashboard, go to APPEARANCE>MENUS and setup/adjust a custom menu.
3. I don’t have an answer about the header. But I was able to get my header “correct” by changing the page width in the dashboard, APPEARANCE>MANTRA SETTINGS>LAYOUT SETTINGS. In the Content/Sidebar width section, change the dimension use to relative and adjust your columns widths appropriately so that the TOTAL WIDTH is equal to the width of your header. Note that the header HEIGHT can be adjusted in the next section of this menu.