Mind me asking what your budget is?
Don’t get me wrong, but it seems you’re just starting out and to avoid biting over to much, it might be smart to look at at least some turn key solutions. Building a custom NAS with loads of drives is fun, but can get complicated.
I’d say get a pre-built NAS if you can afford to and run everything there. It’s easier and has loads of support available.
If you feel like you want more power, then consider adding a NUC or even full server later on and migrate over.
Forget about network speed. Wired is always fast enough. You’d strugle finding new hardware without Gbit these days anyways.
At least that’s how I started and with a N100 NUC running Proxmox now, I don’t see myself needing to upgrade for a long time. Learning Linux along the way is fun.
Good luck!