You should move your music and other personal data to the new computer using one of the methods in this Apple KB article: http://support.apple.com/kb/HT4527?viewlocale=en_US&locale=en_US. iTunes Match is really not the best, most effective or most efficient way to do it. Also, you need to be backing up your personal data to an external HDD. If you are not doing so already, start immediately.
For help with associating the iPhone with the new computer you should post to the Using iPhone forum.