Couple of points to watch out for.
Shoes, try them on if possible.
Shimano come up small, Northwave are a bit bigger and normally wider. But best to go to you LBS.
The pedals have an adjuster, loosen it off all the way before going out for the 1st time.
SH51 are the normal cleat that most use. to release just twist your heel
SH56 are multi angle release.
I use SH56 but thats because they suit me and i like to be able to just flick my heel and be out. some will tell you they are too loose. It really is personal preference.
If you find the SH56 to loose you can tighten the pedal mechanism.