105 lbs and 5"3. Would 400-500cc would be too big for me?

Thank you for the question. Despite your good description of goals, online consultants will not be able to provide you with specific enough advice to be truly helpful. Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging)  as well as careful measurements (dimensional planning) will be critical.





Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant size/profile selection) is:







1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work. Sometimes it is helpful to seek consultation with a few board-certified plastic surgeons before making your decision regarding  choice of plastic surgeon.







2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals. 



In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. For example, 



I have found that the use of words such as “natural” or "C or D cup” etc means different things to different people and therefore prove unhelpful.



Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.







3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery, after the use of temporary intraoperative sizers.







I hope this (and the attached link, dedicated to breast augmentation surgery concerns) helps. Best wishes. 

Hello and thank you for your question.  The
best advice you can receive is from an in-person consultation.   The size,
profile, and shape of the implant is based on your desired breast
size/shape, your chest wall measurements, and soft tissue quality. 
This decision should be based on a detailed discussion with
equal input from both you and your surgeon.   Make sure you
specifically look at before and after pictures of real patients who have
had this surgery performed by your surgeon and evaluate their
results.  
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

It is possible you have some features (e.g. very loose breast skin) that your consultant may be trying to address with a larger implant.  You would be well-served by obtaining consultation with another surgeon before proceeding with surgery.