I did not seed my sandbed, but if I were to, I would start with mostly dry Caribsea sand. Then to seed it, I would buy a couple pounds from various LFS
and then sift through the sand for worms or whatever and then QT the sand for......I don't know.....6-8 weeks, so hopefully any nasties you picked up(if any) would die off, like ich as you mentioned.
That would increase the biodiversity of your sandbed.
180-gallon acrylic mainly SPS, SWC 1A Cone Skimmer, APEX Neptune Controller, 3x MP40w Vortechs, Tunze 6045, Radiums 250w in Lumenarc Minis, Galaxy Ballast, BRS Dosers