The "Queues" tab on Forge is not connected with Horizon. Adding a new worker through the Queues tab results in a worker that runs php artisan queue:work. Docs
If you want to use Horizon and your setup you have in config/horzion.php you would have to start a new Daemon. You can add a new one in the Servers > Daemons tab in Forge.
The command would be php artisan horizon and the directory would be something like /home/forge/example.com/. Don't forget to add php artisan horizon:terminate to the deploy script of your site to automatically restart the Horizon worker after each deployment.
Are these going to be any different to what I have setup within the config. Should I run both or just one of them?
So yes, using using the "Queues" tab results in different queue workers than with Horizon. As you've already installed Horizon I would highly recommend to stick to Horizon and it's config file.