Mac Pro and living with Thunderbolt storage

So I´m thinking of making the plunge and purchase the Mac Pro with 256 or 512GB SSD. So what i am wondering about is what kind of Thunderbolt external storage to buy and how the performance is with thunderbolt when working with larger image files (1-2GB .tif´s). The internal storage wont be sufficent with 256/512GB SDD and the 1TB i to expensive for me. So i would prefer to have a external storage to store images and also to do actual work on.

The computer I´m using at the moment is a 2011 Macbook Pro with a 256GB OSX disk and a 1tb mechanical (swapped the Optical drive).

Backstory: I´m a photographer and retoucher. Blabla. Need a new computer. And so on.