No, it by no means is too broad. Drum Sets and Accessories could be your niche by all means. You might not want to make your website that exact keyword phrase, rather something more brandable though.

When you choose a domain, you are going to want to choose something that is "brandable" versus something that has keywords within it. The reason this is the case is because as you build out your website, you can target as many keywords as you like within the content (that is how you will rank).

I have created a discussion here outlining the process and what to look for when choosing a domain name: How Do I Choose a Good Domain Name? Hope this helps you out and I definitely think you are on track with your niche. :)

I would let my keyword research dictate that. If there is enough low hanging fruit, then you can do well in any niche. That's my opinion anyways.