Usually, maintaining a server doesn't take much time once set-up. I personally use NixOS to manage my server, but it's very complicated, and I would not recommend it to a non-developer. However, there is tools/OS called YUNoHost, that is able automatically set up a bunch of services including lemmy and mastodon.

They also provide a free third level domain name (or can use your own, but do it before installing Mastodon or Lemmy, as it'll break federatio.), but you'll need to provide a server. You can rent one (I use an OVH VPS), but you may also just use a spare computer at home, or buy a cheap one (Everything that isn't a slow HDD should work well). I'm unsure about what capacity you need to plan for storage thought.

You should also probably make sure your ISP provide a static IP (that may disabled by default) and that they allow to configure port forwarding (can be found in the router settings usually).

Also, don't forget to set up an automatic backup system. YUNoHost probably recommend something in that matter.