Welcome to the Mac platform. Although your interests and hobbies will dictate the applications you will need, BitTorrent should satisfy your needs. Search Google for BitTorrent if you are unfamiliar with this peer-assisted digital content delivery platform.
Two popular Mac BitTorrent clients are Azureus and Transmission.
If you want to download music (or anything else) with BitTorrent you can either try the popular BitTorrent trackers such as The Pirate Bay, BitTorrent Monster, Demonoid, isoHunt, Torrentz, etc. or search Google for BitTorrent music.
If you want to know the applications that other Mac users - who share your interests - are using, the MacRumors forums is a good place to start.
