For my home server, I decided to use an Asus board with integrated, passive cooled Intel Celeron CPU (ASUS N3050I-C), which has a TDP of 10 Watt. I think 4GB RAM should be sufficient. The board comes with 2 SATA ports, so I added a PCI express card with two additional SATA ports. The plan is to have 3 hard drives integrated, one for my movies and TV series (3TB), one for my Mac Mini backup (2TB) and one for the MacBook Air backup (1TB). Each of these hard drives should consume not more that 5W. This means, there is no need for a big power supply. I decided to go for the smallest picoPSU available, this has a nominal output of 80 Watt. I choose a 60 Watt / 12V power adapter to fuel it.