The only true “roadblock” I have experienced was when running on the raspberry pi, where the CPU was too slow to do any transcoding at all, and the memory was too small and unupgradable to be able to run much at the same time.

As soon as I had migrated to a proper desktop (the i7-920) I could run basically everything I would regularly want. And from then on it was a piece of cake upgrading. Shut the machine down, unplug, swap the parts, plug in, turn on. Linux has happily booted up with no trouble with the new hardware.

Since my first server was a classic bios, and the later machines was UEFI, then that step required a reinstall… But after the reinstall, I actually just copied all the contents of the root partition over, and it just worked.

The main limiting factors for me has been the amount of memory, the amount of SATA connectors for disks, and whether the hardware supported hardware transcoding.

For memory, ensure the motherboard has 4 sockets for memory, that makes it easy to start out with a bit of memory and upgrade later. For example you could start out with 2x 4GB sticks for a total of 8GB, and then later when you feel like you need more, you buy 2x 8GB sticks. Now you have a total of 24 GB.

For SATA ports, ensure the motherboard has enough ports for your needs, and I would also strongly recommend looking for a motherboard with at least 2 PCIe 16x slots, as that will allow you too add many more SATA or SAS ports via a SAS card.

Hardware encoding is far from a must. It’s only really necessary if you have a lot of media in unsupported formats by the client devices. 95% of my library is h.264 in 1080p, which is supported on pretty much everything, so it will play directly and not require any transcoding. Most 1080p media is encoded in h.264, so it’s usually a non-issue. 4k media however often come in HEVC (h.265), which many devices do not support. These files will require transcoding to be playable on devices that do not support it, but a CPU can still transcode it using “software transcoding”, it’s just much slower and less responsive. So I would consider it a nice convenience, but definitely not a must, and it depends entirely on the encoding of the media library.

EDIT: Oh, I just remembered… Beware of non-standard hardware. For example motherboards from Dell and IBM/Lenovo. These often come with non-standard fan mounts and headers, which means you can’t replace the fans. They also often have non-standard power supplies, in non-standard form factors, which means that if the power supply dies, it’s nearly impossibly to replace, and when you upgrade your motherboard you are likely forced to replace the power supply as well, and since the size of the power supply isn’t standard, the new power supply will not fix in the case… Many of their motherboards also have non-standard mounts for the motherboards, which means that you are forced to replace the case when upgrading the motherboard… You can often find companies selling their old workstations for dirt-cheap, which can be a great way to get started, but often these workstations are so non-standard that you practically can’t upgrade them… Often the only standard components in these are harddrives, SSDs, optical disc drives, memory, and any installed PCIe cards.