They clipped the last part about boarding and pretty much only answered the part about stacking modules. Rob's answer on the show was that you could stack, but not indefinitely. You could makes some inferences here, but he left a lot open to interpretation (thus more forum discussion of what he actually meant).
I recently got a chance to corner Rob in person ( ;] ) about getting clarity on what he meant here. While the 'modules' are meant to represent distinct sections of the ship, they are not individually configurable by the player. There will be Caterpillar variants that will swap out functionality of the sections (likely also including the number of sections) and players will presumably be able to pay to change to these configurations, but they will all be predefined by the developers.
Also, the line in the Caterpillar description about it being the "Freelancer's evil twin" was a mistake / typo, which makes all the arguments on the forums kind of humorous in retrospect. It is primarily a cargo ship (hence the high capacity we recently saw in the ship stats) that is extremely flexible. We'll see where they go with the 'flexible' part. There is some implication of piracy / boarding from the Drake angle and Ben has said in the past that he wanted salvaging to be a focus / variant.
Also, Rob likes vertically launching missiles, because they are cool. We'll have to see what comes of that. :)