I guess it depends on your use case, but option 4 seems to be the most versatile and easy to set up. You can configure the server remotely, and then virtually any user can connect almost any device and copy the files.
Do you happen to know whether CIFS client is not too big of an install? I found this OldWiki article on it. I want to think, "When they have a how-to like that, it can't gobble up too much space." I wonder if there is some general way to find out what any package takes up on being installed. (Don't feel you have to come back to me on any of this. Questions for anyone that might know.)
No idea if there is a better way, but I'd start with looking at what opkg can do to tell you the dependency tree for a target package, and the size of each. I think there may also be a "download but don't install" option, and the space change of the packages on /tmp might be indicative of how much flash would be used.
Do you have a way to push the files from router to end-PC?
If not and each PC is pulling the file then would it be better to keep the files in a Google or Azure cloud repository to get them from directly? A similar approach I've used in the past is to have a cloud repository that a "master" device synchs with in real time as a pull operation, and internal devices use the master device,
How many files of what size will be accessed in what way? A repository of (say) PDFs for occasional read-only access will create very different demands to shared access to Excel files, etc.
You're exploring the line of making OpenWRT a networking and NAS device, which is discussed elsewhere and not (if I summarise correctly) a recommended approach. Having a "proper" storage device maybe with port forwarding to let you access it could be better.
for 21.02 version & samba4 I suggested to plan the possibility of modifying the material which is equipped with SPI flash (8 pins) without much capacity with a memory in 32M but I did not have much feedback on this request
i have modified a XIAOMI R3G with 32M SPI flash and build a new version
Thanks. But you wouldn't believe how un-glamorous my project is. The router will live in my mother's house, and I will be sending her some old movies from before the flood. Until now, I have SFTP-ed into her Windows computer to upload (at some 0.5 MB/sec or slower), but this required her computer to be on all the time. She does not like to have it on all the time, and she wouldn't want a NAS on either. The router's USB can receive the trickling of the movie file until the computer is on and ready. I would think this 'router as NAS' could handle that much, no?
Thanks. I am looking into Wireguard. One of the very reasons I want an OpenWrt at my mother's house is so I could have a second public I.P. address with which (together with my own I.P. address) I could start experimenting on VPNs. To get to that experimenting stage, I have to set up something I already understand, which is SSH.
On that scenario, if the router supports it, I think that the SAMBA server is the best approach.
You can send and manage the files remotely, using a VPN plus any tool of your choice. And you can configure the shared folder as an network drive in the computer, so it's completely transparent for the user.