I don't think those sources are accurate, at least with respect to the E: D universe. Slaves, like all other cargo, follow the relationship of 1 canister = 1 ton = 1 unit. Now I'm not positive that it is affirmatively stated anywhere that one "unit" of slaves is one individual person, but it is nowhere implied that a unit is more than one person.From various descriptions (wiki's and all that). Both a metric or a shipping tonne can store about 12 imperial slaves. Provided they are not too fat.
They must, yes. Attempts to measure them in-game indicate that they are about 2m long, but it's not trivial to accurately measure something that small. 2m is also consistent with how large they appear next to cargo hatches, which are known from exported models to be 5m square. But if anyone has gone to the trouble to export a model for a cargo canister, I'm not aware of it.Two of them fit in my cargo racks if their sizes are 1 x 0.4 x 0.4, with space for scaffolding around them. That's close enough to the right aspect ratio, but the cargo racks would have to double in size if they are 2m long, plus another 25% if they are 1m wide. It that across flats or across points? I couldn't find an authentic reference for that, only a comment on the Wiki. They must have a defined size -- they have a model after all.