There is many hidden quests in Fallout 3 but i there is one when you reenter the vault. (after you father dies) hang around the vault entrance.
You're going to have to be more specific than that. There are lots of hidden doors in Fallout 3.
a quest
you don't.
You find him after completing "Tranquility Lane" in Vault 87. The vault is hidden in "Smith Casey's Garage" somewhere to the west. Just continue on the main story quest and you'll get there eventually.
Rivit City
just continue on with the main quest and you'll be able to do it.
I personally recommend Fallout 3 to any other Fallout game. Fallout 3 has a more organized and in my opinion interesting storyline. And you. And you can also keep the game going after you beat the main quest on Fallout 3 if you buy the DLC "Broken Steel."
If you are talking about the "Trouble on the Homefront" quest its after you complete Project purity. Travel to a relative distance from 101, Megaton for instance, and you will hear the Vault 101 distress signal on you Radio, listen to it and you will then know what to do. Good luck.
yes
The quest Head of State is given by Hannibal Hamlin at the Temple of the Union.
You Buy the "Operation: Anchorage" addon.
yes it is a reward from euligy Jones in an unmarked quest