You are right, the ore normally goes to a mill to be upgraded not to a smelter. Potentially a high grade ore(7% Ni) could go directly to a smelter, but it could not go by airplane because of its low value.

Normally a roughly 2% Ni ore goes to a mill and typically is concentrated to about 15% Ni(8 to 20% range depending). This means that the nickel is concentrated in a product which has a weight only about 1/7 of that of the ore itself. The remaining 6/7 of the ore has to be placed in tailings dams or partly returned back into the mines as back fill.

The 15% nickel concentrate then will be sent and processed in a smelter, and then finally to a refinery. For the ROF this will certainly be in Sudbury. Building a new smelter and refinery costs about 3-4 billion $

One big issue related to milling is the tailings containment which is like a 'hydrodam'. You need to contain this sufide(iron sulfides mainly) rich material to prevent sulfuric acid formation and leakage to the environment. Water flow, rain amounts, snow conditions, etc all have to be well documented and a good spot has to the found before these can be approved and built.