What exactly do you mean by "keep the angle at 45 degrees"?
45 degrees refers to the angle or "elevation" in which the section is held to be cut: your stylist will know exactly what that means.
Should I bring my own sulfate-free shampoo, or is it likely that they'll have one there?
Do bring your own sulfate-free shampoo; although it is becoming more common, it is still unlikely the salon will carry a sulfate-free line unless they do a lot of curly heads. If you are worried about what they will say, use this trick: tell them you brought your own shampoo because you discovered you have a sensitivity to certain product ingredients like sulfates. They probably won't bat an eye.
Also, how much of a difference in length should there be between the longest layer and the shortest layer?
The difference in length between the longest and shortest layers depends on the overall length of your hair, and is really difficult to judge unless we can see it. If your hair is already long and you would like to go longer, make sure you emphatically let your stylist know to keep your shortest layers at chin level (with the exception of your face frame, which should be cut separately).
Hair Stylist and Curly Hair Specialist - St. Petersburg, FL (Tampa Bay)
Blog: Live Curly, Live Free
Facebook fan page: Live Curly Live Free
Sulfate- and non-water soluble silicone-free since 04/22/2002
3B, brunette: medium texture, low porosity, high density