After having all my files in a windows server and a Linux server, I've thought that it could be a good idea to have a server to have this files saved and make some automatic tasks, such as having a torrent, running some batchs and (why not) storing my personal cloud.
In the actual stage of this project, I am searching for a board.
My first approximation was the Raspberry PI, but eventually I gave up this approximation due to the little capabilities this board has.
The second approximation was to look for the size this board could have: there are dozens of sizes of boards out there, but I think the nanoITX is a good size: it's 12cm x 12cm, ideal to make a barebone with just a big hard disc (probably two with redundancy) and nothing else. Other option could be a Mini-ITX board, 17cm x 17cm: this is a bit bigger, but probably it could give better performance.
The third was to pick up a good board, now I am looking at this: Asrock QC5000-ITX/PH. It has a good price and practically everytinthing I need but the wireless, but I think a wifi dongle could make a deal. And apparently it work with linux.