Hi @facthenrio,
Thanks for your interest!
Nexus Kingdoms is designed primarily for PvP gameplay rather than co-op.
If you're looking for a co-op experience where players can each build and develop their own spawn together: Oarc Multiplayer Spawn
Oarc was specifically created for that purpose.
Nexus Kingdoms was inspired by that concept, but has been expanded significantly with mechanics focused on PvP, diplomacy, territory control, and kingdom warfare.
Regarding your questions:
Players keep their own kingdom and progress when they disconnect.
Additional rocket silos can be built if needed.
Space Age planets are shared between players and kingdoms, rather than each player receiving a separate version.
Compatibility with overhaul mods such as Krastorio 2, Space Exploration variants, Rampant, or Deathworld has not been extensively tested yet, so compatibility cannot be guaranteed.
I hope that helps. Feel free to ask if you have any more questions!