Expansion
The player may not expand more than worlds worth 100 points a year. This either means you can colonize two colony worlds or annex one minor world by whatever means you like.
If the player wages a succesfull war of conquest against another faction or an NPC faction (remember, those are controlled by the mods), this does not apply. The spoils of war are to be determined on a case-by-case basis by the mods.
Every three to eight years gametime (exact time period to be decided on a case to case basis by the mods) the players will get 400 instead of 100 points of worlds. With these, the players can either:
a) Raise an average world to major world status and add another 200 points of worlds or
b) add 400 points of worlds.
EDIT: Please note that this does not affect the usual means of upgrading a planet via trade pacts.
Please note as well that these are extra points, not represented or taken out of your budget. However, the player may chose not to expand and then add those points to the budget.
EDIT2: In case it was not clear before: You cannot save expansion points. You have to use them to either upgrade or gain planets. No partial upgrades, no partial ownership.