A small forum will work with a 40 GB disk, no additional space needed.
It was the same for me when I started my Discourse journey. I never used Linux or SSH.
Providing a how-to about how to connect to your server hosted by a certain provider might be a bit out of the scope of this support forum, but anyone is free to help, of course.
When you create a server on Hetzner, you’ll have the choice between using an SSH key file or a regular login/password (it will be generated and sent by email if I remember well).
Plenty of guides on the internet will describe how to connect to a server via SSH. The goal you want to achieve is to access the server’s command line.
As for how to connect the domain to the server’s IP, it’s done through the DNS management from your domain name’s provider admin interface.
If you’re willing to pay for help, you can post in Marketplace 