To my eyes, the most promising open source e-Commerce platforms I've seen lately are Ubercart and Magento. We're actually currently using Ubercart here as I write this, for this very site! Ubercart is actually a module for Drupal (a powerful content managment system). Drupal has another e-Commerce module... Drupal e-Commerce (yes, not very imaginitive, I know), but it's not currently quite as full featured as Ubercart.
This article has some excellent ways to use caching in Drupal, to make your Drupal site perform better:
I found a nice article on how to make nice artist/band sites with Drupal. It lists the modules you could use, and even gives examples of Drupal sites that other artists that use Drupal. If you're a musician, a site made with Drupal could be the ultimate way to promote your music:
Oh, and where is the best place to host your new music site? AccelerHosting of course! ;-)