Header vs Logo

There's no difference - just different names for the same thing.

Let me know if you need more info :)

Can I eliminate some of the white space between the masthead and navigation?

Absolutely.

The easiest way is with our Spacing add-on in "Customize > Element Spacing".

If you don't want the add-ons, you can use CSS:

.inside-header {
    padding-top: 0px;
    padding-bottom: 0px;
}

Adding CSS: https://generatepress.com/knowledgebase/adding-css/

Thanks!

You're welcome :)