WordPress.com will perform just as well as any other Managed WordPress host when it comes to a site with lots of images and music.
That said, no matter where you choose to host your site, you’ll want to follow best practices to reduce the size of your images as much as possible.
These days, search engines like Google are penalizing sites that take a long time to load. If you’re using full-resolution images on your pages, your site will take a long time to load. And that will translate to lost visitors, and lower rankings in search engines.
And generally speaking, background music is a sure-fire way to increase your page load times unnecessarily, plus potentially annoy your visitors who may already have music playing in their own environment. I would recommend against using auto-playing background music on your site.
If the main purpose of your site is music, then make those audio files as small as possible (i.e. MP3 files), and add them with a regular player, so your visitors can choose when they want to listen to the audio. This tutorial shows you how to add music to your WordPress site.
To your final question, our videos are created using the open-source version of WordPress available at WordPress.org. We don’t have video tutorials for the proprietary version of WordPress that is only used at WordPress.com. They have their own video tutorials for their product.
Hope this helps!