I have a Beaglebone Black (BBB) and here is what I can tell you...
As you probably already know, the chip that handles HDMI output on that
computer requires a non-free driver... as far as I know that is the only part
of the board that requires non-free software to use. For server applications
like you are describing, this is easy to work around. You may even find this
desirable if you are using a USB wifi dongle as the HDMI signals can
interfere with the wifi... it is quite simple to disable:
https://learn.adafruit.com/setting-up-wifi-with-beaglebone-black/hardware#hdmi-port-interference
(In this context, "cape" refers to a daughter board for the BBB ... at boot
time the board can try to figure out which "capes" it is wearing and
configure itself accordingly... the HDMI is in a sense implemented as a
built-in "cape")
BBB has a built in eMMC flash chip as well as a micro SD card slot to be able
to expand its storage... I don't recommend using the eMMC for storing your
data as it can become corrupted if not shut down properly... if possible I
would recommend putting the OS on it mounting it read-only... then mount the
SD card as read-write for your data. Or you could just run everything off of
the SD card, which is how I have mine set up right now. In any case, you
will want to back up quite frequently in case your SD card starts to wear out
or something like that.
One thing to understand... it is not a fast computer. It is a single core
1GHz processor which is plenty powerful for running a simple personal server,
but may be disappointing if someone thinks that they can use it for all kinds
of things. As long as you understand that and don't try to do more than it
is capable of, you could definitely use it as a personal server for the
things you mentioned.
