First I’d say, out of experience, only have room for 2-4 drives in the enclosure, and not have the ability to exchange to a faster CPU, can quickly become an issue for a homelab/NAS, especially when plex is in the mix.
I was recently in similar situation as you. I decided to spend a while scouring eBay for some decent offers and get a sense of the market. From having built several home servers for myself over the years, it’s not worth it, it’s way too expensive compared to used enterprise. The quality of equipment you get from enterprise is simply higher, and you’d get a lot more from there than building a server from scratch yourself.
I ended up getting a Dell T320 Server, 16 GB RAM, 1x Xeon E5-2407 4-Core cpu, 2x450W PSU, 2x Gb NIC, 8x 3.5" Hotswap SAS/SATA, for €300. Over the following month, i managed to get a 10 Core Xeon E5-2470v2 for €32, 64 GB ECC RAM for €100, 2x 8TB SAS 12Gb for €250.
I didn’t care too much about power consumption, but i was very surprised when I saw it was only using 65W when running 9 docker containers I use in the home for this and that, among these are Emby Media Server, Docker Registry, MySQL dev server, Transmission/flexget and openvpn so friends and I have merged LANs, and a few others for this and that. Within the next month or two, I will move my bitbucket server, a few websites and a handful of APIs to my home server from AWS, and maybe 2-3 VMs running some test OS’es, and I doubt it will be too much for the server to handle it.
It is so quiet that I can’t even hear the fan running, and it’s standing 30cm from where I sit. At the same time, there’s also the benefit of iDRAC, which allows me to connect to it via a web interface, even when it’s turned off. Here I can remote shutdown/restart, monitor everything within reason, setup raids, do BIOS changes, and a lot more, without connecting anything other than power and network. iDRAC would allow me to install the server somewhere in a corner where it’d be out of the way.
Only thing i regret, just a bit, is that I didn’t go for a T420 or larger, for dual processor, it’s not something I really need, it’d just be nice. Who wouldn’t like to see 40 cores in htop.
There are also some other factors that are good to take into account for when building a NAS. Raid 5-6 on anything larger than 2TB drives is a bad idea due to the probability of another drive failure on a rebuild. Think it’s in the area of 4% success rate when having 4x8TB in Raid-5. Not the best odds. Therefore, room for more disks is a benefit in the long run, seeing that you’d be able to run a reasonably sized Raid 10 or similar.
Also, enterprise equipment is built to run 24/7, when properly maintained, they can do that at 100% utilization for a very long time without problems.
Just my 2 cents.