I can offer assistance on the Yuffie question. Everything else has been answered well.

If you are so far in the game that you can enter the crater, then you cannot do the Yuffie Sidequest. The Sidequest is available until you face the Turks a final time in the Midgar Tunnels. After that, any and all optional appearences of the Turks will no longer be available (that includes Wutai and the Gelinka).

And I have to reaffirm what's already been said: You cannot, in any version of the game Final Fantasy VII, revive Aeris. Ever. It is impossible.