shortcut to turn screensaver on??

Not sure that you got the answer that you were looking for so . . . . go to the Desktop & Screen Saver System Preference panel. Select the Screen Saver Tab/Button. In the bottom left corner is a button that says "Hot Corners . . .", click on that. From there you can choose which of the four corners of your screen that you can designate to Start or Disable (keep from starting) the Screen Saver or select several Exposé options. Once you set the corners to do what you want, such as activate the Screen Saver, then all you have to do is move your mouse to that corner and there you have it.

I hope this helps.

I don't know. If it doesn't yet exist, you could define one in Preferences/Keyboard shortcuts.
I prefer to use an active corner of Exposé (mouse in the upper left corner)

I prefer to use an active corner of Exposé.

Same here eddy, in my case I chose the bottom left

If the OP has not heard of Expose, then do a search of it in Finder. It is a very handy tool.