Discourse hosting =/= self-hosted
i am an experienced self-hoster and have done some complex configurations; as well, i used to work for Discourse, so i have some insight into the two concepts, which it seems like you have a bit mixed up. i will try to clear some things up for you, but this is by no means an exhaustive explanation, even if longwinded lol. i don’t know where you got that flow chart from but it isn’t really correct.
Discourse hosting is what it sounds like - Discourse will host your site for a fee, and as you have already discovered, there are different priced tiers, starting at free, that offer more options as you go up, and enterprise is the top and most expensive (it gives you the most options as well as their top-of-line support team services and custom design and development options). managed hosting is the same (Discourse hosting is a form of managed hosting), but also offered by other partner companies like Communiteq or Literate Computing. these partner companies also offer various development and support services for a fee apart from hosting (as do i). keep in mind work is not usually free for development and specialized support, and this is what the Marketplace is for. Also, while the Discourse hosting prices structure may seem expensive to you, i can assure you that many well-known companies pay them top-dollar for their very large, busy and well run enterprise forums, many of them private. the SLAs and levels of support / development services that Discourse offers them are such because their business activity demands it. for example, if you are a tech firm or financial organization and you are hit by a DDoS attack that can cost your company 6 figures in downtime and loss of services, or you require a very customized professional interface for a large number of employees, then paying enterprise hosting is well-worth it.
self-hosting means what it says - you are hosting your own site on a rented server (or a physical one you own, which i don’t recommend because that is another advanced can of worms). self-hosting isn’t just renting a server (or VPS - virtual private server) and ssh’ing in and there you go. there is some knowledge that one has to have in order to be a self-hosted admin. a beginner coder who’s built a few wix websites isn’t going to do much for you from a self-hosting Discourse perspective; very different things and skill level. the fact you don’t know what SSH is yet is probably an indicator that you have some growing to do in that area. Secure Shell - Wikipedia
if you are interested in learning, i would suggest you begin by reading the standard install documentation and learn the ropes from there. some find it easier than others, and the fact you have some website admin experience may help you learn faster. just being able ssh into a server is one thing, but you have to be comfortable in a command line interface and understand the basics of docker admin, and how containers work. since you say you have a small site, then a standard install will probable work fine to start from, and it will give you access to all the built-in plugins, plus any others you might want to add; essentially, a self-hosted Discourse instance is like having your own enterprise level Discourse hosted forum but without their expert support and uptime SLAs and performance (for example, you will have some downtime every time you re-build or do updates, but Discourse hosting does this for you and without any descernable downtime).
there is no reason whatsoever that you cannot learn how to self-host, but remember that nothing is free and what service and scale you want will determine what cost you will need to pay. some VPS services are cheaper than others, and there is a list here that @pfaffman has put together that can help you decide. for example, i have 3 Discourse sites, all on Hetzner, but with different sized servers and costs associated with them: 2 sites are dual-container installs behind Cloudflare CDN with R2 (S3 compatible) object storage for uploads and backups, and the other is a standard install used for testing purposes. i have used DigitalOcean before but it can be relatively expensive; however, it is the recommended starting point for those learning standard installs (although i don’t actually find Hetzner that much different, and i prefer their dashboard).
if you do not want to pay Discourse or any of their partner hosting companies to manage your hosting, and you need more than the free tier, then my recommendation is to do some research and reading, then try a self-install. learn what an app.yml file is and how to edit it, how to setup your nameserver and email services - this is the starting point for learning how to configure your own discourse instance as a self-hoster. some VPS services will let you rent servers quite cheap for short periods just for testing or learning.