1.
If you want to disable Cart button deactivate WooCommerce and Cart button would go away. In case you want to keep active WooCommerce but just want to disable the cart button then add this CSS in wp-admin >> Appearance >> customize >> addtional CSS
.navigation .btncart {
display:none;
}
3. To change navigation colors please go to wp-admin >> appearance >> customize >> header >> header styling and there you can play with available options.
4. To disable Top Bar please go to wp-admin >> appearance >> customize >> top Bar >> styling and disable it.
2. This would need you to make the change in the theme file which you can copy the desired file in same template folder to child theme then make your required changes.
or you can add this CSS to wp-admin >> appearance >> customize >> additional CSS
@media screen and (min-width: 64.0625em) {
.header .large-offset-1 {
margin-left: 0px;
width:18%;
}
}