Rackmounting these is tough, because of cooling, and don't even try to get a small form factor motherboard. You'll almost certainly end up with an EATX case. You could choose units, you'd probably end up with 3U or 4U, from
this list or look for regular EATX cases (usually marketed as server cases). Of course, there's always the opportunity to screw yourself, so verify the form factor of the motherboard and case before ordering and make sure you end up with the right power supply.
For how to set these things up, look at how major vendors do it. Be conservative and redundant, have extra room and good circulation. Don't try to be like BOXX with the 1U Renderboxxes.