A small thing but quite interesting: if your configs have negative values for the GC planet dimension IDs (like the defaults, -28, -29, -30) then players will be able to make Nether Portals on the planets.
If you change those IDs to positive values - which is totally fine, it won't break anything in GC - then players will not be able to make Nether Portals on the planets. This is in vanilla Minecraft which disables Nether Portal creation in the End or any higher dimension ID. For the exact same reason, Nether Portals cannot be made on Space Stations. (It's possible some other mod or plugin can change this, for example Enhanced Portals 2 mod, but this is vanilla behaviour.)
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This raises another point - what happens if the server and the client - which can both set GC planet dimension IDs in their configs - do not have the same config settings? The answer is that in GC3, recent versions (since 3.0.2.182), that should be no problem for Galacticraft which will still happily transport the players to those planets using rockets or /dimensiontp. But it might be a problem for other mods teleporting (e.g. Mekanism) or for Bukkit teleporting (e.g. Essentials) which I guess might produce client-side crashes in some situations. The easy answer is that clients must make sure their planet dimension IDs are the same as on the server. We are still working on a proper answer to this.