I agree with Simon. "I've spilled coffee on the table" just tells us where the coffee spill happened - it happened on the table as opposed to 'on the floor' , 'on the desk' or 'on the sofa'. It could be a quite a small spill. "I've spilled coffee over the table" gives more information: its suggests a more dramatic accident, covering a larger area. If you say that, it tells us that the spill went over most of the table.

I would naturally say no 1 - on the table but I could also say: I spilt coffee all over the table - more dramatic, bigger mess :)

Over the table sound better.

Hello. Well, in this case, if you're talking about the table just like the "surface which we put the things", i think "over" is better.