How do I safely transport a heavy item downstairs?
Well all your prep work sounds good but I am well over 100Kg and I would want another person on the stairs below to help by actually pushing back on the freezer so it doesn’t drag you down the stairs. The model I use has belts that when you pull it back the belts ride on the stair edge and don’t tear up the stairs. But even with this I consider it a 2 person job. Unless you have an electric stair climber hand truck.