To give you some information about developing boards... If you are using Eagle to design you board, here is another thread that contains schematics for building Leonardo clones. On important thing mentioned was the selection of the crystal's package. http://arduino.cc/forum/index.php/topic,78631.0.html
I recommend watching some videos at Sparkfun and Youtube about SMD soldering. I had never did SMD before building my small Arduinos. I was happily surprised how easy it was....I had thought it was for "super solder gurus" rather than a hobbyist like me.
Here is a bunch of tutorials for using Eagle ..I have no affiliation with the video maker: Cadsoft EagleCad Tutorial Lesson 1 - YouTube