I think to remember that only the first 20 aircraft ( all mk1000 ) had this fat rear cargo door. The thinner door located a bit further back was introduced after that and was standard on all later F28 aircraft.
The paxdoor in its present situation was introduced after lots of complaints about the steep stairs when the aircraft had low fuel loads and few cargo in the hold. People had problems with the slopingdown of the steps. The present steps got have an extra folding step at the bottom. The second handrail was an option the airline could buy. Later it became standard. The folding plank in the doorway was an option for the airline the wanted to unload passengers via an passenger boarding bridge.