Did a bit of research, and going to try and get the Bequiet cooler upgraded (Pure Slim seems to basically be a quieter stock cooler equivalent) and some faster RAM but other than that very happy with what I ordered; it should cover all his general purpose well, he can throw in a storage drive from his old PC, and then he will be sorted
Update: Sorted!
This is what he is getting:
Phanteks P300
5600X /w Dark Rock 4 Cooler
Tomahawk B550
16GB HyperX Fury DDR4 3600 C17 (Micron-based so will hopefully overclock to C16 or 3800-4000 C18)
Zotac 1050ti 4GB
WD SN550 NVME 500GB (faster SSD would be wasted, but I'll put it in the slower NVME slot so he COULD get a faster/larger NVME later)
BeQuiet Pure Wings 2 (Top Exhaust Fan, will match the cooler)
2x NXT AER P 140mm Static Pressure Fans (front SP fans, due to the restricted intakes)
Antec Earthwatts Gold 550W 80+Gold PSU
Should be a wonderful system for day to day and hopefully on the quieter side!
He's not REALLY a gamer, so the 1030 will cover all his desktop/video decoding/light game dabbling and other graphically accelerated shenanigans, and the CPU with the decent cooler should PBO clock nicely and at relatively reasonable noise levels!
Updated - swapped the PSU to a slightly lower power model with higher efficiencies, Seasonic as OEM and much longer warranty. Was only £10 more so worth it.
Update 2 - managed to snag a reasonable value 1050ti.