Yes you can do this, it's in the defensive pre-snap audible adjustments (see your manual for this one as I don't recall this off the top of my head)
Yes you can hot route your WR when you play online. If you mean change the hot routes themselves I believe you can but it must be done in your profile before you begin the game.
Yes you can, how you are pressing the joystick when you throw is going to determine where it's thrown. For example if you are throwing deep to the WR on the left and you press up and left really hard when you throw the QB will throw toward that sideline and lead him. Try this in practice mode, if you really press hard up it may lead your WR way too far for example, so you need to learn "touch" on your throw and how to place the ball.
Well on PS2 it is press hot route (triangle), the person you want to hot block (like X for your RB), then press R2 and he will adjust so instead of running a route he will hot block. However in some cases you can't audible someone to hot block for instance on a play action pass you obviously could not tell your RB to hot block.
Hope this helps..