I am looking to have a custom build of a unix OS preferrably FreeNAS with robust features and media service out of the box. I will provide more details to the winning bidder to keep it confidential. But to understand the scope of work, I would say that all the required features are already offered out of the box in FreeNAS and open source media server softwares like Plex - Most of your work will go in making the solution automated (possibly shellscripted) and finetuned for better user experience.
The platform ideally is ARM based but can be Intel Atom based only if really required.
System will have around 512/1024 Mb RAM and flash storage possibly 16-32GB. Raid features will require extra storage connected via SATA/USB3 etc.