Regarding the baggage capacity of the Caravelle, we worked Varig's (first with jets to South America) up at KIDL (KJFK) and they had to have a main deck baggage compartment which I believe the Comet also had. That would certainly cut into the space for passengers.
There was indeed an E and E compartment forward of the forward baggage. You could access it through a belly hatch but not from the baggage hold. The forward air stairs actually retracted into this compartment when retracted. By the way, they were of excellent design compared to others I saw and worked.
The mechanical control cables were routed under the floor as were the heavy generator feeder cables and wiring looms.
The APU was in a compartment aft and was relatively easy to change. The pneumatic system and the air conditioning system were aft of the rear pressure bulkhead in the tail compartment and quite accessible.
The rear pressure bulkhead was a source of corrosion and structural problems not helped by lavatories against it. This is not uncommon in many aircraft types.
The composite tail cone was jettisonable for emergency egress use. Depending on whether the aircraft had rear airstairs or not, you either pulled a plug type hatch or opened the aft bulkhead door and proceeded along a catwalk in the rear compartment. The tailcone could be released from inside or out and a small slide then was used for exit.
The external emergency release handle looked very much like the rear airstair operating handle. In one week at KEWR the caterer popped three tailcones on us (EAL). It was not appreciated as the fall would damage them.
I often wondered if Douglas had sized the fuselage to that of the DC-8 as Boeing did the B737 to the B707, if Douglas would have survived.