With Eye of the Storm and Thousand-Year Storm on the battlefield, I cast Lightning Bolt. Storm count goes to one, and Eye exiles the Bolt. Through Eye, I copy and recast it, and Thousand-Year Storm copies it once. Storm count to two. This much makes sense.
Now I cast Shock. Copied twice, the original is exiled, and my storm count goes to three. Now Eye copies both Shock and Bolt. Are these two cast in order (so one is copied three times and the other four), or do I cast them simultaneously, only choosing their order on the stack (and copying each only three times)?