Transfering all my song to my new computer

Question

I have recently changed from PC to Mac and I'm want to tranfer all my songs to my new computer. I'm trying not to lose any songs,
30% of my songs were purchased on my Iphone (I know I can't transfer them through Itunes)
40% of my songs are from my CD collection that I had tranfered onto my PC way back when
10% purchased from Amazon years ago
20% of my songs are from various other "non-official" sites such as youtube and the such
If I copy all my PC & non-official songs onto an external hard drive and then transfer them onto my New Mac, then add them to my new mac's Library, then sync my Iphone with the same Itunes account I used on my PC, will I lose all my itunes purchaced songs?
Itunes is asking me if I want to sync my Iphone to my new Computer, but I want to make sure I don't lose the songs I paid for.
Of if you have a better why for my to mergy my music, please let me know.
Thanks in advance,
Anniehow

Answer 1

As for transferring purchases from the phone, you can: 
iTunes Store: Transferring purchases from your iOS device or iPod to a computer - http://support.apple.com/kb/HT1848 - only purchases from iTunes Store
To make sure your library transfers intact:
Quick answer if you use iTunes' default preferences settings:  Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive.  Open iTunes and immediately hold down the Option (alt) key (shift on Windows), then guide it to the iTunes Library.itl file in the moved iTunes folder.
If you put the copied iTunes folder in the default location of Macintosh HD > Users > *User Name* > Music  then you don't even need to start with the option key held down, iTunes will automatically look for it there.  (Make sure there isn't anything already in the iTunes folder there that you want to keep since you will be replacing it with the one you are moving.)
Longer answers if for any reason you do not think all library files are inside your iTunes folder (changed preferences settings at some point):
iTunes: How to move [or copy] your music [library] to a new computer [or another drive] - http://support.apple.com/kb/HT4527 - a somewhat bewildering and not always easily understandable set of options.
For the record there's this reference for iTunes 11 but it really doesn't strike me as having the specifics you need. iTunes 11 for Mac: Move your library to another computer - http://support.apple.com/kb/PH12168
2011 ilounge article: Transferring your iTunes library - http://www.ilounge.com/index.php/articles/comments/moving-your-itunes-library-to -a-new-hard-drive/  - An article with good background information (similar to the links above), particularly if you are not sure your media files are all grouped for quick answer above. Unfortunately under the single term "transferring library" it describes two very different moves; relocating just your media (not  really transferring your library and not recommended unless you really need this configuration), and relocating media+database (really your whole "library").  Make sure you understand the difference before electing to move only media.