Hiding sidebar and header from startpage

.home #secondary {
    display: none;
}
.home header#header {
    display: none;
}

To add CSS: use the “Additional CSS” option in the customizer. https://codex.www.ads-software.com/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools to help you see and test changes to your CSS.

once you have content on the hoime page, which you want to spread out over the existing width, you might also need to add:

.home #container.two-columns-right #content
{
  width: 100%; 
}

Thank you so much <3 It works perfectly!