Structure Blocks in Bedrock have a major difference from Java's Structure Blocks. In Java, you use the Structure Blocks to save and import structures you've made. While in Bedrock, these blocks work entirely different. You can upload your builds to a website called Remix 3D. That's where you can post your builds and look at others. Here's a video about it by Mojang: https://www.youtube.com/watch?v=mfPBNnL2kdM
I've had multiple tears in the ground in my racing map me and my friends have built. They also looked like unloaded chunks until you fall right through them.
Yes. This is a feature. One turtle eventually lays 1-4 eggs on the sand after breeding. If there is no sand nearby, turtles will not lay eggs.