£5 for a USB NIC - £100 £3 for a PoE to 5V DC splitter - £60 £2 in short cables - £40 Shelf? £20-50
PoE Switch I already have spare Leaf switch I already have spare Network storage I have in abundance.
Cost wise it's not prohibitive, about £250
I think the biggest worry is, as you say, it might not be the most stable or impressive compute.
There are plenty of examples of Arm machines running at scale now, so that's a pretty narrow perspective.