Purpose of Drain Plugs

[peterb]

I asked this question a while back and will ask it one more time.

I have a 1978 23' SF.

Up top I count four drain plug holes: two in the stern and two up front [one under each hatch.)

On the bottom I count another four drain plugs: three in back and one up front.

Here is my multi-part $64k question:
Am I correct in assuming that I should always have the three in the back plugged (that is whenever the boat is in water)?
Which drain plug feeds my saltwater wash down (the bottom drain plug up front or somewhere else)?
When I leave the boat at the dock unattended should I have the two drain plugs up top (and in the stern) unplugged, in case it rains?
While underway should I plug the two stern holes or not (no dirty minded repsonses please!!)