Custom menu items in admin

Use the add_meta_box() function (working example), and use nav-menus for the post-type. John Morris also wrote about this in 2013: How to Add a Fully Functional Custom Meta Box to WordPress Navigation Menus.

code to add an extra selection to the menu editor

The WooCommerce Brands plugin has this feature. https://woocommerce.com/products/brands/ It sounds like you would need to move your brands out of the custom field and into this plugin, so the effort will depend on how many product brands you have and whether you’re willing to start over with this plugin.

Cold Fusion to WordPress

You need to learn about the WP concept of Templates and Themes. Themes are how pages are “built” and styled, and take content from the WP database as the page is Templates are part of Themes, and describe how a page specific page is built. The database is where all content is stored, including Media … Read more