HTML in menu

Hi there! I have a few questions that i hope someone can help me.
The first one is that i´m only working with the side menu and disabled the main menu, but the side menu doesn´t open children categories. Is there any way for the side menu also open the children categories?
As i disabled the main menu, now i have the an empty space in the top that i would love to costumize, how can i put a module, or html in the place that the menu was before?

Hope that someone can help me.

My best regards

Same problem