Hello,

To change the width of the categories menu dropdown you need to add the following Custom CSS in the Custom CSS for Desktop area under Theme Settings >> Custom CSS.

.header-categories-nav .header-categories-nav-wrap {
width: 200px;
}

You can adjust the width accordingly.

2) You can populate the HTML Blocks as you want by editing the HTML Block for the specific menu item.

If you are trying to ask anything else then provide with some relevant screenshot of the specific area to check it myself and help you out accordingly.

Best Regards.