Skylake SP has just barely enough PCIe lanes to hit your requirements in a single socket, but you can build one cheaper and probably lower power consumption than an Epyc system. There's an X11SPM-TF on ebay for around $300 with two x16, one x8, one m.2, plus dual 10GBase-T ports. Just add a $20 Xeon Gold 6132 or $100 6150 and another $100 or so for 6x16GB ddr4. My dual 6132 desktop with a mid-range GPU, four various NVMe drives, and single 10GBase-T card idles around 100W, a single socket should do somewhat better.
Edit: there's also an X11SPI-TF currently available cheaper, the PCIe layout isn't really any better than the Micro ATX X11SPM, but it does at least have DCPMM support if you get a Cascade Lake CPU.