Starter Pack I gives you the IA house early.
Starter Pack II gives you the Atomic Age house early.
In EA, without Starter Packs, you'll be having 12 workers.
If you've already bought Starter Pack I, you'll have 14 workers. You won't get a house for gold (under the Economy tab) upon reaching IA.
If you purchase both Starter Pack I and Starter Pack II in EA, you'll have 16 workers. You won't get a house for gold (under the Economy tab) upon reaching IA as well as AA.
The Estate can be purchased only for real money, and can be purchased anytime, which will add 3 workers.
In Atomic Age, constructing the Sydney Opera house will provide an additional worker.
The Chinese get an additional worker from the beginning of the game.
Hope this helps.
Please let me know if you have any questions, and we'll be glad to help out.
Cheers and happy gaming!