I've never had an issue using Osmocote+, and I've been using it for many years without it causing any deaths, or causing an ammonia spike. Remember to get Osmocote Plus 15-9-12 this is the one that has macro/micro nutrients, it doesn't matter if you can get your hands on the old series or the new outdoor indoor series, the only major difference between the old series and the new series is the old series had calcium, and the new series does NOT have calcium in it.
2" should be enough substrate to hold it down, you can either go with ice ferts where you put some osmocote+ pellets in an ice tray add water and freeze, or go with empty capsules that you fill with the osmocote+, either way just make sure to push the osmocote+ as deep as you can in the substrate. I usually put 3-5 osmocote+ capsules around each sword plant depending on size, and 2-3 around crypts.
15g Fluval Flex - Will be a planted shrimp tank