You interview is for the position you have applied for. To apply for the freighter fleet, you are applying for a direct entry FO slot. Therefore the minumum experience required is much higher, I believe these minimums are published on their website... basically you need heavy jet time. CX don't employ SO's for the freighters.
In the past the freighter fleet was all 747 Classic (-200/-300 series) I have heard they have introduced some -400's recently.
The pax fleet consists of B747-400, B777-200/-300, A340-300/-600, A330-300.
I don't know exactly the difference between lifestyles with the pax/freighter crews. With the freighters, you have more of a choice of bases, I think they have a couple of US basings, I'm not sure where though. I assume most of the freighter flying would be back of the clock type stuff with not as many overnighters compared with the pax crews.