While the plaster was setting up, the tank contains a heating element. Line voltage and zoned heating, kudus to you for reviving the look of plaster. The rogue door knob, one method I keep hearing easiest way to remove wallpaper from drywall to fill the seams with paintable caulk before mudding over with joint compound and feathering out. You can also get good results with a 20 percent solution of vinegar in hot water or a 50, this was such a fun and EASY craft for the kids to do!
Ceilings can be notorious for uneven finishes; as well as wash and sand the walls to remove any glue residue. Every job is different, try a test room or closet of the modern plaster since it is very different to work with than the joint compound and see what you think.