As rPi 4Bs are hard to get still / overpriced, unless you’re absolutely married to the rPi, check out OrangePi 5B for a much faster CPU, more RAM, eMMC, and good wifi OR get the 5+ for the same minus wifi (it has an E-key m.2 to add it) but adds a 2280 m.2 so you could throw a 4TB m.2 SSD on there (which are about $200 now) and now you’ve got a pretty dang good little NAS that’s fast and fanless for about $350-400 all-in. Did I mention the 5+ has 2x 2.5G Ethernet?