Morning of or matside weigh-ins most you should cut is what you can sweat off during normal warm ups, so probably 2-3 pounds.
Night before you are probably safe cutting 5-9 pounds, depending on size. I would only cut if you have done it before and you respond favorably to it. Even then, a lot of times divisions are combined, so it sucks to cut weight and then wind up in the same division anyway.
In terms of dealing with nerves, map out your game plan on paper. How you see a perfect match going, how you would respond if people stop or frustrate your perfect moves. Then visualize yourself in these scenarios. Visualize success.
Beyond that, just focus on doing your best and having fun. It's all a learning experience that will make you stronger win lose or draw.