Relevant rules are on p.133 or Total Warfare, and p.239 of the Tech Manual.
Question 1: Is there a functional difference between five 1-ton/crit cargo items and one 5-ton/crit cargo item? For example, could five 1-ton slots mount a single 5-ton object?
Question 2 refers to this sentence from p.133 of TW: "If a critical slot containing cargo is hit, all cargo in that location is destroyed."
a) If a 5-ton/crit cargo item receives a critical hit to one slot, are all five tons of cargo destroyed?
b) "All cargo in that location" from the passage above seems to imply that a single critical hit to any cargo slot will destroy all cargo in a unit's location (eg: the left torso), even if the cargo is in different 1-ton cargo slots. Is this correct?