If you search 't' internet, you will find someone very helpfully saying "oh, yes, you can run these outside a chassis but it's difficult - I'm doing it" but not explaining any further.
This board works fine with 12v, 5v (standby) and 3.3v powered. Fortunately my boards came with the risers and full trays. If you just have the board, you'll need to find somewhere to tap these in. 3.3v may only be required by the riser for the SATA / SAS repeaters.
There is a little wonderful design niggle - the ATX style connectors are NOT the normal pinout, 12v and ground are reversed. If you get the fan / power distribution board, it does work but I've not discovered how to power this board on correctly - power good never comes up and the motherboard complains about it - and will not start up. Fortunately, clip the red wire and power good has a pull up (or down, not looked).
Upgrade to the latest firmware including the FRU update and you can customise the number of and performance of the fans as with most Intel boards. The supplied fans really are little screamers and will run quite balls to the wall when it detects the chassis has 'failed' (or has mysteriously gone missing). There are 3 pairs of 2 fans in the normal configuration. When you do the FRU update, it detects what is connected to the board and stops complaining.
Power button is on the edge connector if you have the riser. It's momentary.
Intel, unlike most others supplies full pinouts in their downloadable PDFs.
These are really, really nice boards IMHO - if you don't need excessive RAM. Standard 2011 square heatsinks. LOM works. Jumpers are a tad annoying to get to (my boards came BIOS password locked). I'll post the pinouts and download links later, although they are quite easy to find. Will also get power consumption details, but these are in-line with other 2011 server boards - it's mostly the chips.
Good luck!