It's not bad. But I think you want to add too much too quickly. You're talking about possible gems to trade, multiple new biomes, new mobs, etc. While none of those strike me as immediately horrible, I need more detail for all of this before I support any of it. The ideas are nice, but just like any idea, the way they're implemented can make or break them. While you are obviously putting work into this, the suggestion just seems shallow at the moment, having a lot of ideas, but not going deep into why we need all of them, and because of that, it isn't much better than a lot of ocean suggestions, and doesn't give me a good idea of how this is unique in any way.
I like the basic idea, but I think it could be more fleshed out, instead of "here's this generic mob that should be here to make the oceans more exciting". I think you could make the ideas more unique and minecraft feeling than just having a couple animals and structures made out of blocks.