It'd be a nice idea to show the game prototype - the name of the Amiga game you're trying to implement, best if youtube link too. Because I can't grasp the game mechanics from your description except that: There are planets, each has some resources. Player builds ships and mines resources to get new tech and build other ships and battle drones.
Seems like Reuinion, right? That was a nasty game

About your questions:
1. Why would all planets want to know about each other? You have X, Y of the planet, you have the ships, you move ship to X, Y and if it coincides with any of the planet it mines resources.
2. Why do you need a messaging system? Each ship just comes to X, Y and if there is a planet there, it mines resources.
3. Read a bit about "game cycle". It's usually fine to have T: Double and adjust it by dT := now - LastTime each frame if not paused.
4. What do you mean by "resource management"? You mean Lazarus resources, or planetary resources?

What experience do you have in programming?