How many B747-400 with PW4056 does Cathay currently have?
3
I found 3 so far: HKD/E/F formerly operated by Singapore Airlines. Is this correct?
Yes.
Is Cathay supposed to get 3 more with PW4056s in the future or no?
Certainly getting more not sure on the exact numbers. Also getting some off SAA. (RR powered).
Do any CX 747-200F's have Nose Cargo Doors?
Yes, RR powered ones do CF6 powered don't.
I believe all 400's have the SCD's?
All 400 freighters have side cargo doors, wouldn't be a freighter without it.