Simple NAS

RPi4 2GB has been adequate for my needs, all of my MC devices are 2GB. 4GB for $10 more gives you a lot more headroom, if you're on the fence then I would spend the extra money.

But even at 2GB, Kodi sits under 1GB (usually around 800MB with a very large buffer cache tunable). A fresh start up of Kodi is less than 350MB of RAM used, but things go up as icons are cached, and then the playback buffers add in as you play content.

I do occasionally playback 4K HDR movies, no issues, but most content I have is 1080p. I don't use SSDs, all of my media is on my NAS. I just boot from an SD card.

Now that I am re-reading, I seem to have missed the question, it's not about using it as a MC device, but as a NAS. I have no experience with that, but I can't imagine it being great, really depends on how demanding the clients are.

By the way, what I would suggest is looking at the RPi5, and maybe check out some of the performance reviews / NAS testing from folks like Jeff Geerling. RPi4, in my opinion is very much built to a price point, and some of that sacrifice is I/O bandwidth. RPi5 specifically has a custom chip to address this shortcoming, and adds a lot more bandwidth to USB3.0 and even a PCIe bus for NVMe's.

I'd say thats a tough question. And as always, it depends on your needs or rather expectations. Although I never tested it by myselfe, I would expect the RPi to work properly. There are plenty of guides in the www explaining how to use the RPi4 with OpenMediaVault... Important would be to have it wired. Don't expect WiFi to work stable.

What I can say is, that the SMB/CIFS share LE provides, works just fine. I use x86 hardware but there shouldn't be a difference. Drag an drop via SMB works perfect even from macOS to LE.

So if this is the only thing you want to achive, I guess it will work just fine. RAM doesn't matter so much if you are the only user. I mean - your HDR files are greater 2GB or 4GB anyways, right? But keep in mind, that SSDs can die and that you don't have redundancy of data.

I don't want to sound like a granpa, but a (single) NAS is no proper backup target!

IMHO if users want a NAS they're better off aiming for a lower-spec Synology box like DS223J which is purpose-built and easy to expand in the future to include a second drive for data redundancy. The cost difference vs. an RPi4 + PSU + Case really isn't so big and it'll be easier to use and maintain than a homebrew RPi device, and there's no rats-nest of cables and PSU's to deal with. If you do want to go down the RPi route look at OpenMediaVault or similar (NAS distro) unless you plan to use the other RPi for playback too.