How do I sync and iphone 4s and ipad mini to a new Mac with my iTunes saved on external hard drive?

I recently bought a Mac from a friend of mine. I got rid of my old PC. Before doing so I copied my entire itunes to an external harddrive. On the new MAC, i imported all my music to itunes from the external hard drive. I then logged into my itunes account and downloaded all my apps i purchased. My questions is...I want to sync my exising ipad mini and iphone 4s to the new computer. Should i forsee any problems? (ie. losing/erased songs or apps?) Also My contacts were saved on my itunes, and I dont want to lose those either. Is there a way to sync both without losing anything?

Thanks!!