Unfortunately, the custom fonts with
@font-face rule will not show on your Font Manager. If you're willing to pay additional amount just to see your fonts on Font Manager, then I suggest you use Typekit.
Please refer to this guide to help you get started with Typekit:
Our builder has a feature called Element CSS that caters adding CSS of your needs on a specific element. Here's a guide on how to use this:
Hope this helps.