3TB Time Capsule or a 3TB Hard Drive??
Early TCs had power supply problems... but that appears to be cured.
I personally use TCs and like them because they seem to remain stable across Apple's maintenance upgrades. Apple "officially" does not support NAS backup to drives attached to an Airport Extreme. People get it to work... but there have been too many stories of it breaking with various OS updates. For me, I just want it to work and not be a finicky hobby.
I also strongly recommend that you subscribe to one of the many offsite cloud backup services. I was a Mozy fan for many years. For the past 3 years, I have switched to Crashplan+. These are dirt cheap... extremely secure... and give you automatic off-site backup and disaster recovery.