If I complete this mission, I win but any other investigators lose...

We always play with the cards revealed... this mean that we must play with the cards covered? or the other player can see this card and try to obstruct me?

Cards are revealed for everyone to see. And if you should be both willing and able to go through with the mission, the other investigators might want to try and stop you—if they can figure out how.

Of course, the last time I saw someone try this mission, she went to kill monsters to have enough to recruit at Ma's. She went insane and got "Paranoia." It was marvelous. Serves you right you traitor.