Hello Juan and welcome to the Q&A Board. I think your questions can be answered by the article here specifically about
memory cards.The short answer to your first question would be simply that you can get more images on a memory card that you can with the typical built in memory. As to your second question, the highest capacity card should be detailed in the specifications for your camera (if there is a limit) and shouldn't be a function of the amount of built in memory.
