Synching iPhone and iPad with new iMac - former pc user

I'm trying to determine to most efficient way to set up iTunes and synching of my iPhone 4 and iPad on my new iMac. I am finally moving away from using a pc and am facing the issue of trying to preserve all the content on my devices as I set up the iMac. I'm ditching the old oc iTunes library. The iMac will br the primary (and only) iTunes library going forward.

I realize I'll need to manually transfer mp3 files from the pc to the iMac (those ripped from CDs and not purchased on iTunes) and re-establish the library. But how do I avoid losing all the aps and music I purchased on my old pc as I set up the iMac iTunes?

I'm also interested in saving the contacts I've built on my iPhone - using that as the basis for my iMac contacts.

I have no intention of using the pc again -- fully realize you cannot synch to two iTunes libraries.

Any suggestions on how to begin to minimize hassle and minimize any file loss is much appreciated!