Reference the question how much do I overlap - never really think that much.:-)
I tend to look thru the view finder and look for points that stand out as some feature that is prominent - tree - rocks - line of a wall  etc so that either CS2 or I can match up.
I never consider how many shots I will take.I look for several prominent points and take as many shots as I need to fill the whole scene - maybe three - four - ten - whatever. 
Sometimes a pice just wont match no matter how you try,edge of a lake or something so heres a tip i do.
Yes some will say its cheating - I cal it artistic license.
If a but just wont match I select the frame that the piece is in.I use say the lasso tool and and select it - feathering the edge.Then copy and paste it on the image I am working on.
Then use the rectangle tool - hit control and T - and turn or adjust the peice to fit - it works.
One other thing I do is before taking a shot I have the camera set to aperture priority ( merely for depth of field ) and take readings over the whole area I am going to shoot.
Then if the readings vary I take a test shot at a mid reading to see the results - if wrong try again.
When I am happy with the reading I set the camera to manual and take the whole set of shots on manual. 

Hope this helps