My personal recommendation is to get started asap with what you have. That would mean using any old thing you have laying around. Do you have an old laptop? They are ideal for beginner self hosting as you can physically access the machine and it includes a battery backup right in the machine. Usually they are also fairly lower efficient, so that is nice too.

Buying dedicated hardware acts as a barrier to actually doing things, so getting past that is key. If you find you don’t actually want to do self hosting you can just stop using your old laptop, but if you bought a full server machine it will be a bit of a trap and make you feel like you failed in some way. Also, the cost right now is fairly prohibitive, but using existing hardware can make that much more manageable.

As for what to run, I would recommend trying a fresh install of a distro based on Debian, Ubuntu, Fedora, and Arch. Yes, four. They are different and have a different feel to them, but also have different communities. By going through the process of installing each one you will get a feel for the system and the community around it and have a better idea what works for you. I spent a few years having around the Debian end of things but eventually moved over to Arch stuff and am currently using EndeavourOS. Your experience will likely be different to mine but trying a few different options will help you figure it out.

Then moving on to services. Try to see what you actually use your machine to do now and then find services for that. For example, if you use something like Google Drive to synchronise data from your phone to your desktop then try using Syncthing to replace that. If you use Netflix to watch stuff try using Jellyfin. If you do play things like Minecraft get a local server running.

These will all be for learning, so their performance doesn’t need to be better than what a professional can provide, they just need to work and be yours to learn with. If you find you love doing this and enjoy the process but the hardware is holding you back this is a good time to upgrade to a dedicated machine.

For this I would recommend getting an office computer like an Optiplex or similar, just a basic office computer with an i5 or similar. You will want a fairly good amount of RAM in it, probably 16GB minimum and really 32GB is where things start getting good. A dedicated graphics card is not likely to be useful this early as the iGPU in most modern processors is actually fairly robust and should handle transcoding video for most use cases at a small scale. Storage could be one SSD for the OS and multiple spinning disk drives in a RAID or similar configuration for storage. The SSD will make the actual OS faster, decrease boot times, and make it faster to install and update things making updates less disruptive. The spinning media is way cheaper and you can backup all of your OS drive onto the spinning disks as a cron job in low usage times.

That’s my two cents on it, start with what you have, expand as you need but not aggressively before you need it, and try things now before you are too afraid to mess something up because you rely on it. Remember to have fun and experiment, nothing teaches better than experience. Enjoy yourself, don’t take it too seriously, and don’t lock yourself in to one specific thing, be flexible and willing to experiment.