Whats the best way to setup this small homeserver for my needs?

I installed arch (https://github.com/warpme/miniarch) on one of those small android tv boxes (A53 Cpu and 4gbs ram) that usually come with android+spyware and vague promises of piracy and i want to turn it into a small homeserver. I dont really know anything about servers so I dont know where to go from here. Im planning on connecting a 1TB drive to the box. I want some folders from my PC and phone(specifically documents) to be synced to the server automaticly whenever both are connected to my network, but I also have a ton of audio books, ebooks movies that I obviously only want to be accessible (by my TV, ereader, phone) but not synced accross devices. Ive also been thinking about having shared compute running in the background (seti or folding@home or something else). Obviously everything should need as little maintenance as possible, i want to have it sit in a corner and be able to forget about it. Could you point me in the right direction? Thanks in advance