Will iTunes match download all my music to a new hard drive?
If you enable iTunes Match, your entire library (up to 25.000) songs will be synced with your iCloud. So all your songs are in the iCloud. You can add a device to the iCloud and by so, all your music on the new device will be synced onto the new device. That's how iTunes Match works.

If you computer/hard drive gets stolen, you buy a new one and authorize it with you iCloud, it will sync once again on your new device. 

So yes, you'll be able to download all your music stored in your iCloud onto new device. 

As a matter of fact, even when the original device lost it's files, the songs are still stored in iCloud.

But be aware, the limit on devices is set on 10. So make sure you haven't add 10 devices already!

EDIT:
Proof of this is on the iTunes Match-page