I’ll try to answer your questions although I think you may have some over-lapping terms leading to some of your confusion.
When folks on this forum refer to ‘self-hosting’ Discourse they are referring to running an instance of Discourse on your own server. (more on this in a minute) When they refer to ‘managed hosting’ they are referring to a service which provides an instance of Discourse running on hardware the host also provides. By ‘managed hosting’ they mean the instance of Discourse is managed by the service, they handle keeping the Discourse instance updated and the operating system Discourse is running on updated and running properly.
To ‘self-host’ Discourse you need a server which has access to the internet and a properly configured DNS service pointing at your server. The server can be real hardware running on your premise or it can be a ‘VPS’. A VPS stands for Virtual Private Server. A VPS is server hardware provided to you which you have total control over as if it was on premise but you access it ‘remotely’. By ‘accessing it remotely’ I mean you use tools such as SSH and FTP to access the server, control it and transfer files to it.
SSH is ‘Secure Shell’. A secure shell is basically a command prompt running through a secure (encrypted) tunnel. Are you familiar with running a server from the command prompt?
Shell, terminal, command line and command prompt all kind of mean the same thing. Running a computer using a terminal window and typing in commands at the prompt. If everything I just said sounds like a different language this might require some learning before attempting.
When you rent a VPS, you are provided credentials and the IP address of your new server. Usually when you purchase, you are given a chose of operating systems. You log on to your server using a terminal program such as PuTTY or just the terminal window on your computer. You can use a FTP (File Transfer Protocol) program such as Filezilla to transfer files from your computer to the VPS
So once you have rented a VPS and logged onto it using your SSH you can then install an instance of Discourse on your server and then you will be ‘self-hosting’ Discourse. You have full control over your Discourse instance and the server it is running on. You can usually keep Discourse up to date with the built in administration tools within Discourse itself but occasionally you will have to use the command prompt to update manually. You also need to keep backups of your data and know how to restore them. Discourse makes backups automatically but you must download them and store them securely in case you need them.
With a VPS you will also have to maintain the operating system your Discourse instance is running on. This requires some knowledge of the operating system and how to keep it up to date and properly running. If you screw up the VPS usually all the VPS hosting service is capable of doing is wiping out your operating system and reloading a fresh version. You also have to backup the important data needed should you need to reload the operating system.
Once setup and running, this is a fairly easy thing to maintain, if you know what you are doing. From your description of your skills I think you could handle it. The best way to learn how to do all this is try. Renting a VPS is fairly inexpensive these days. Set up a server, try to get Discourse up and running on it and come here or ask.discourse.org if you have questions.
Just bear in mind if the forum you run doesn’t get a lot of traffic, which it won’t all on it’s own, if you screw it up you can just start over. If a bunch of people join your forum and start posting then you will need to keep it maintained and backed up. If you have a pre-existing forum, or a product you want to promote or support maybe check out a hosting provider. If you are just goofing around and learning… go for it