Depends entirely on what you're using the device for and how (if at all) you utilize networked (NAS, cloud, etc) or external storage. For me personally 256gb would be way more than needed, since I have nothing that would take large amounts of storage on local device.
Also, 1x16gb will halve your memory bandwidth, get a 2x8gb kit
1x 16gb would allow cheaper upgrade to 32gb later if that's something OP is concerned about.