1st, i would not recommend using a time capsule as the location for your precious iTunes media files because
- you can not use time machine to back up whatever is stored on the TC's internal drive
- if there is a problem with the TC, it will be very difficult to retrieve the files from the TC's drive
2nd, you don't have to start with a new, empty library. copy the entire iTunes folder (not just the iTunes music or media folder) from <MacintoshHD>/users/<yourname>/music on your Mac to the new location, then launch iTunes while holding the option (⌥) key, click on choose library when prompted, and select the iTunes folder you copied to the new location.
if you opt for a NAS, i would recommend this particular model (what i'm using) since Synology products are very Mac friendly. setting it up in a RAID 5 configuration provides additional protection in case a drive fails and the on board backup software lets you back up the RAID to an USB drive.