All depends on how much stuff you are putting on your phone. You have around 27GB to play with before you need to by a memory card.

I plan on using up the internal memory first and then buying a 16GB micro SD card if i need to.

Not too sure about the benefits of using a micro SD card, but i would assume that the devise can read/write to the internal memory faster then a microSD card. This is why I will using this first.

Hope this helps