Freenet is built around similar ideas, combined with encryption an anonymization. Which hopefully adds the benefit of you not being legally liable of distributing CSAM. The gist of Freenet is that you can operate a freesite or upload files, and the content is redundantly dispersed in encrypted parts among a number of other Freenet peers. They don't know what they're hosting and neither do you, the client just fills up the allotted space and uses some bandwidth, that's all.

https://en.wikipedia.org/wiki/Freenet

Regarding of how easy to make something like this network, I'd wager it's pretty hard. There will be a lot of questions, even while establishing the happy path, for example how you manage the updates, especially when you update the protocol, not just the software, and how you effectively manage the volume of search requests, how you distribute the files etc.

And then there's the abuse the network will inevitably get. How you handle spammers, CSAM, malware, ISPs that throttle/block you, the legal risk you put your clients up to, etc. Nice big can of worms. To begin opening it, I suggest a reading through Wikipedia's Peer to peer file sharing article, and especially the File sharing modal on the right, which nicely captures the ideas that have been tried so far.

https://en.wikipedia.org/wiki/Peer-to-peer_file_sharing