Quite a few recommendations echo the same sentiment: get a whatever computer, start by installing xyz Linux, and go from there. Instead of direct recommendations I'll present some alternative paths you may find useful to balance your self-hosting style against.
Path 1: Get a cheap VPS and host something like File Browser to transfer some low-stakes files between friends&family. Add services and beef up the server as you need. Doesn't matter too much if it gets hacked, it's separate from everything else and you'll learn to harden it over time when you learn to consider an exposed server insecure by default. Also your financial stake is really low, sub 5€/month and you can quit at any time when there's no unique data on the VPS. Grow your stake slowly along with your confidence in how well you can secure the thing.
Path 2: Get 3 identical 1-4TB drives and an SSD boot disk on some random computer, and install TrueNAS for home use. It has a large self-hosting community and nicely abstracts away the Linux side of things. No worries about exposing ports, just host anything you're okay using just at home. Think: Jellyfin, Paperless, Home Assistant. You might find this useful if you never intend to really learn Linux in the first place and just want to solve some of your digital problems locally with some money invested. Later, add a mesh VPN like Tailscale or Netbird to safely access it from outside your home.
Path 3: Get heavily into networking and start by getting complete control and understanding over what happens in your network. OPNsense, adguard, OpenVPN/wireguard, pihole, ddns, ids/ips, VLANs. Do this if you're a control freak and are willing to commit to updating your stuff and keeping track on potential attack vectors.
I started out with path 3, but have moved more or less towards a mix of 1 and 2 and no longer expose ports on my home router. If I'll end up getting more than one device, I'll probably install TrueNAS on one and make the rest a baremetal Talos cluster. Now my stuff runs on one device so it makes most sense to be Proxmox, this is however not advice, I work in tech and full well realise this is not an easy system to run.
I'll have to add that if going for path 1, be sensible and make sure you know if you have been hacked, to not expose your friends to malware by accident. You might even want to host a honeypot for learning this part.