There's a great variety of chinese motherboard/cpu combos from the likes of Erying and Toptonwhich have 6-8 sata ports, a PCIE slot and a variety of CPUs. Cores are more important for a NAS than speed ...
Asus' TUF Gaming GT302 PC chassis supports the company's Back to the Future (BTF) cable-hiding scheme and offers great cooling, offset by ho-hum noise control in its stock configuration.