Can an iPad work to replace a computer in terms of photo management?
There are numerous hard drives that will work with the iPad. Some wireless, others via USB (with the camera connection kit). The lightening port is a whole other thing if you end up with the 4th gen iPad, though there might be a workaround.

Here's a 1TB wired solution from HyperDrive

Here's a 500gb wireless solution from Seagate