I wouldn’t add the media with snails. That’s a guaranteed way to get snails into the tank and you’ll never get them out afterward. I normally move all the media from the old tank some of the old water and add fish right away. Since you added feeders already you should have a bio load to sustain the bb. I wouldn’t be adding and rotting shrimp at this point. Watch your parameters very closely and be prepared to do a water change if needed. I would just wait it out now and once you see the ammonia go zero pull all feeders and add your fish.