I Am 5'5 1/2" 125 Pounds is 450cc Going to Be to Big?

Choosing a size that will make you happy is somewhat challenging.  If you have experienced pregnancy, then you already know what size you liked.  If you are still concerned about your size choice, I suggest using rice in a knee high nylon stocking to create 'sizers' for you to help you see what you are going to be with your choice. 

1 cup of rice equals 240 cc, 1/2 cup 120 cc. 1 and 3/4 cup would be 420 cc's and would be very close to what you are considering.  Use a stretch cup, unpadded bra to help with sizing.  Whatever size you pick in your bra needs to be up-sized by around 10% to create the appearance you have with the sizer in your bra cup over your breast.

Being excessively large is not good so your concerns are valid.  I believe you should find some reassurances using this home sizing method.  Good luck!  Oh by the way, the biggest complaint I hear from my patients is "I wish I went bigger".

This is a tough question to answer - especially without a photo of you and your measurements.  The same size/profile implants will look different on different women depending on your frame and muscularity.  I would definitely recommend trying on a range of implant sizers with an unpadded bra.  This will give you and your surgeon a good idea of the size you would like to be.  He or she may still recommend a different size for your implants to give you the look you want.  Breast enlargement is not an exact science.  It seems like it should be simple to say I'm a B cup now and I want to be a C so what size/profile implant should I use, but it isn't that easy.  I recommend choosing your surgeon carefully.  Make sure he or she is board certified in plastic surgery, look at lots of before and after pictures and inquire about how frequently he or she performs breast augmentation surgeries.  Once you are confident you are dealing with an expert who has given other patients results that you like, rely on his or her expertise.  Breast augmentation is a popular procedure and most of us perform tons.  That gives us lots of experience with implant sizing.