I’d need to see the code you used to add the custom field as well as the code you added to the
card.php file. I did review the code you posted, but I need to see just the code you added.
If you want, I do provide custom development services. So I could do this for you. If you are interested, use the contact link at the very bottom of the page and I give you quote.
As for the Widget Pack. You can follow the general instructions for installing an extension.
Configuration. Navigate to the WordPress Widgets admin page under the Appearance admin menu. Now, just like any other widget, you can any of the Connections Widgets to the theme’s sidebar. All the options for the Connections Category widget are fairly self explanatory but if you have any specific questions regarding it, let me know.