Figure why it is overflowing. Unplug it, pull out the stopper, or call a plumber.
A clogged drain most likely.
Stop filling it up.
No, you should keep and reuse the old sink.
you put baking soda and smosh it and drop it into the water and it should sink
stop placing the cigarettes on the sink
This method worked quite well on our sink. Put baking soda around the sink hole (it should clump up and slightly go down the drain). Then add a bit of white vinegar and flush around the sink. It should bubble and your sink should be unclogged. If it didn't work you can repeat till it's unclogged.
You should check your sink pipes if there is something clogging the pipes and creating that pressure. If you are unable to locate the problems, you should contact a plumber to inspect your sink.
Yes, if you didn't have them, accidental overflows would go all over the floor.
Well depends on what sort of damage you mean....if you mean damage to your house:The worst that can happen is that your bottom floor will be like a fairly large puddle or if it is all carpet then it will ruin your carpet. But if the sink overflows on the second or top floor then the water will go through the ceiling and ruin it forever.
Chemicals
It depends on the amount and how tightly packed it is, but it usually should sink(natural)
Take the pan to the sink.