I'm more into 6th and 7th gen iPods. These unforunately are missing the iconic click wheel in favor of a tiny touch screen. The 7th gen even has Bluetooth 4.0.
Trying to build one myself[1] with Linux, Rust/Slint and 3d printing made me realise what an engineering effort it took to build a device running more than 12 hours of music playback with a 220mah battery supporting ui animations - all that more than 12 years ago. My nanowave approach draws ~330ma, which would require a 2000mah battery to run 6h from full to dead.
I'm in the process of analyzing the TinyEmbedded Dual[2] to have better efficiency as my current solution (LicheeRV Nano) but progress is painfully slow because i have pretty much no free time and have to learn 3d printing, PCB design and Rust at the same time.
However, I think today it would be possible to build an iPod at home if you have the knowledge and time. Probably you're better off just using a HiBy R1 (which uses Linux under the hood, I already managed to compile my Rust/Slint player for it)[3]
1: https://github.com/nanowave-player/nanowave-ui
2: https://github.com/yuansco/TinyEmbedded-Dual
3: https://github.com/yetisoldier/Hiby-R1-Audiobook-Mod/issues/...