Most modern motherboards have 4 sata ports, or 6 ports with 2 "degenerate" ports, using old PCIE x1 gen 2 ASSmedia chip [most MSI boards like this]
ASROCK has some 8 sata ports boards that use Intel SATA, i use one for my unRAID.
Listen, im also a hoarder, i had more HDDs than actual letters for them in windows 11, eventually i decided that its far cheaper, easier to build 2 PCs, one using huge case that has many HDD slots, but economical CPU [ i have 12700 non K with E cores disabled in BIOS] and install unRAID os, its easy to use OS, 120USD lifetime license.
Its OS for data hoarders, and it allows you dedicate Parity drives to protect your data, to be simple about this, i have 20 HDDs, some 14Tb some 16Tb, and 2 parity HDDS, meaning i have 2 drive fails, each parity disk equals one drive fail you can have, you can have as little as 1 parity or as many as you want, people usually use 2.
Its not a RAID system thats why its called unRAID, each disk is by itself, there is no speed boost from parity.
But the OS is for sharing and managing files.
You can have SATA/NVMe SSDs drives set as cache, so when you copy something to unRAID it copies to SSD and then automatically on timer it copies to the HDD share, for you its invisible and you get the benefit of SSD speed.
If your friend is not a heavy gamer, you can uild him a second system using one of those tiny cases or buy a minipc for day to day usage browsing, if hes a gamer then build him a small ATX build, asrock has prebuilds with case, mobo and PSU, all you need is CPU, RAM and video card
My PC and unRAID connected with 10Gb internet, so for me accessing data on unraid feels the same as if the data was local, also you can stream directly from unraid