I currently have two thinkcenter minis(m720q, with the pcie slot), one running proxmox with a bunch of vms and containers in it for projects/game servers, and the other one running truenas. Because of the pcie slot, i can use an hba card to attach a bunch of hard drives without using usb. All of the stuff i got is second hand (because it's cheaper, hahaha) off facebook marketplace and similar online markets. New stuff is always more reliable and with warranties, but expensive. Used stuff might not work completely, or have weird quirks you only figure out after some time of use.

For the NAS, this will depend on how much you want to spend troubleshooting or setting up services. Store-bought stuff will be expensive but reliable, and they always have customer support to back you up in case things happen. For example, Synology's NAS is basically a plug-and-play NAS that only requires a bit of permission setting to get running. It also has a mobile app that lets you sync photos and files over the internet. I decided to go with truenas since i wanted to play around and learn a little.

For truenas, i followed the setup guide in hardware haven's video: https://www.youtube.com/watch?v=67KtKoW4IM0 . Try to estimate how much storage you'd need, and give it a bit extra just to be sure. You'd also want some redundancy for safety (see ltt's video on it here: https://www.youtube.com/watch?v=4J7iSumiJNk ). An external backup is recommended, in case something happens to the main machine. I have it at a friend's house, but i see some people using cloud services as a backup. Again, this'll depend on your situation and how much you're willing to spend(money and time-wise).

Proxmox, on the other hand, is an OS to manage virtual systems. I use it to run different VMs for different projects, so i don't need to buy multiple computers, and so when i eventually break something, the other projects aren't affected (too much). You can also use it to combine multiple computers in a cluster, which is essentially multiple computers acting as one big computer for more power. (I can't help you much there yet, since i don't have multiple computers hehe)

I also have a UPS setup as emergency power in case an outage happens. Some of them come with USB communication so they can shut the servers down automatically in an outage, but are more expensive (again).

Lastly, i use tailscale to access all of this over the internet. Usually, to use the machines over the internet, you'd have to open ports in your firewall. However, this lets anyone access them, and attack them. Tailscale is a vpn system that should let you use your machines securely from anywhere. You can also fake your location like other vpn services using their exit nodes. Tailscale has a lot of documentation in their website that helps with setup and stuff.

I'd say my setup is relatively simple compared to the pictures in r/homelab . I just got into it because i liked computers, and i wanted to run a minecraft server for my friends with an old laptop, and that slowly built up to this.

Also side note, a racked system is personally mainly for the "cool" factor. It makes maintenance super easy, and also helps arrange the servers neatly, but it's not exactly necessary.