Add font to Typography & More visual customization for Menu

This should help: http://docs.generatepress.com/article/customizing-the-google-font-list/

What exactly could be more advanced about the menu customization?

Fonts> I mean other than Google fonts. To be directly added to Typography

Menu> I mean more options like Transparency. Also, it would be great to change menu item background colors look like rounded buttons rather than square blocks

Other fonts need to be added using @font-face: https://css-tricks.com/snippets/css/using-font-face/

Full transparency is achievable in the menu by deleting the background color. Semi-transparency for background colors is coming in the next version.

This might help for rounded menu items: https://generatepress.com/forums/topic/rounded-navigation/#post-53826

Thanks

How can the menu back ground color be deleted?

Simply delete the value in the background field in Customize > Colors > Primary Navigation.

For rounded menu items, I used this css mentioned in your post, it only gives me the left side of the left item in a rounded shape.

I was more like looking for all menu items have rounded back ground

.main-navigation .menu li:first-child a {
      -webkit-border-top-left-radius: 15px;
      -webkit-border-bottom-left-radius: 15px;
      -moz-border-radius-topleft: 15px;
      -moz-border-radius-bottomleft: 15px;
      border-top-left-radius: 15px;
      border-bottom-left-radius: 15px;
}

I am looking for something like this http://www.mehradgroup.com

Try this:

.main-navigation .main-nav > ul > li > a {
    border-radius: 5px;
    margin-right: 5px;
}

It's almost perfect, only the BOX which contains primary sub-navi items opens to the right (instead of left), putting sub-items of one primary item under a different primary item

sorry this was for another post, my apologies

Thank you for the css

.main-navigation .main-nav > ul > li > a {
    border-radius: 5px;
    margin-right: 5px;
}

You're welcome :)