PCIE to SATA or NVME?

[WoodenBleachers]

I’ve been looking at building myself a small, budget server, and ended up settling for a  prebuilt on eBay.  The device has two pcie gen 3 slots, one x16 and one x4.  My question is: in order to pack this thing full of drives, should I use a x4 to 6 SATA expansion card or get something for NVME on the 4 lanes and then get a PLX NVME card for 4 more NVME in the future?  I’ll be running trueNAS if that’s of importance.

Thanks for all the help!