When you activate a cheat then it normally lasts till you switch the game off.
yes, gta4.net has all the cheats, not many cheats are in the game though.
Certain Cheats disable certain achevments.
no aeroplane cheats :'/
No cheats.
no, you can't
yes you can but sadly with cheats
Yes.
you have to dial phnoe #s
can do that, have to start a new game. sorry bud.
as soon as you get to drive roman yes you can
no
gta4.net has them