If I wanted to use the Polaris to haul cargo, can I use the hangar bay for that? What about swapping out the torpedoes for additional cargo space? If so, how much cargo do you anticipate can fit using all the space available to me?

The torpedo bay is non-modular, and will not be replaceable, as the ships main purpose is to bring firepower. Strictly speaking, you can put whatever you want inside the hangar bay as long as you can make it fit, but the issue you may run into is the lack of cargo plates, like the ones found in the cargo hold, that allow you to attach your haul to the ship. You may find that cargo floating away when the hangar doors open in zero G. While we may investigate after-market options to prevent this from happening in the future, there are no plans to do so at this time.