It looks like you did the correct thing when you installed Windows 8 on your 3TB drive. What I might be concerned about is the "Migration" to which you refer.

I don't use Paragon software, but have you given any thought to copying the OS partition from the old drive to the new drive. If you were using Partition Wizard, in order to copy the partition, you would need to boot to the Partition Wizard (or Paragon) CD/DVD and then delete the current Windows 8 partition on the large drive and copy over the old OS partition in its place. This type of operation is sort of experimental, but in theory it should work. Anyway, you seem to be in a position you could try as long as you did not put the original install at risk.

I would also suggest you not be online during these trials.