Don't forget white balance needs to be consistent for all the shots as well: leaving it in auto will cause color shifts between member shots.
I'd also advocate getting a stitching package that can use enblend to blend over the seams, rather than trying to do this manually.
Hugin is open source (read: free) and can automatically call enblend.
Autostitch is another free package to consider, if you prefer more of a push-button solution.