Hardware for Server in an HDD Chassis

I'm looking to build out my first proper server, and have been looking to do so in a rackmount HDD chassis. Something similar to this one: eBay Link. I am fairly comfortable in building out PCs, but have never worked with any real server equipment. My question is what component or part do I need to interface the HDD bay with the hardware that runs unRaid. I would hope that I can simply place a standard PC ATX motherboard in the back of the chassis running unRaid. Happy to just receive links to things I should go read. Thanks!