[...] it's stated in your terms that a Forum here can host no more than 250 while @SKevo emailed me that one of them hosts 5K as well.
The 250 user limit is not enforced by us. It is the average maximum amount of users for all forums that FreeFlarum can handle. You can go above that, as there is no check to control whether or not a forum has more than 250. When it becomes a problem, we will let you know and ask you to move elsewhere, or reduce your user count.
The limit is probably not relevant at this point because we host a couple of larger forums that operate normally. There is just no time to update the documentation with new information in more detail, at least not for me because I am overwhelmed with my own duties at the moment.
Can anybody please provide me a detailed step-by-step (preferably with pictures) of how to self-host a Flarum forum using any hosting provider?
There is no perfect, general, illustrated, step-by-step guide for every hosting provider, because they all have different UIs, different options and settings that you need to tweak in order to get it working the way you want.
But here's what you should know:
- If you use shared hosting, you might not have access to composer or SSH, which complicates things a lot. Try to seek hosting that supports SSH access (preferably via a client like PuTTY)
- There are many guides on this forum and online, which I've already linked in my E-mail. In general, you will need to pick a good hosting and then do some research on how to setup Flarum on that host. Try looking through the Hosting tag
I'd like to point out that the link that meetdilip posted is an official documentation written by the Flarum team. If you picked a host with SSH access, then it indeed is not too difficult, because all details on how to proceed are described there - please, be sure to check it out. And if you're stuck, you can always open a new discussion on this forum with detailed description of your issue, and I am sure that someone will assist you.