That gravel will still be heavy, even if you drain all the water. Were you not going upstairs, it'd probably be OK, but with the trip up stairs, I think you are adding unnecessary risk. What are you trying to avoid? Uprooting plants? If the gravel shifts or the tank falls you will do more than uproot the plants!
I suggest draining the water as suggested by running a hose all the way to the bottom glass pane. Then scoop pull the plants out to a bucket of tank water. Scoop out all of the gravel to another bucket.
The filter does not need to be submerged in water, just kept wet, so just put it dripping wet into a bag and seal it, it won't dry out and it will have lots of Oxygen that will be missing in a bucket of water.
Another bucket for the fish if you didn't put them in with the plants, they will be happy with the plants if there is room. A cheap styrofoam ice chest is great for fish and plants. No need for more tank water than is in the fish bucket.
Now, with it all broken down you have the luxury of time to set it all up correctly (level, scaped well, all cords and extensions run the right way). Add an airstone and heater to the fish bucket, and some Prime or Amquell, and dont feed them for 2 days before the move. They will be fine for many hours.
This way, you are not risking all the gravel and plants suddenly shifting to one side and stressing the glass enough to crack. Then, while a tank might be cheap, it is a problem to run off and find at a moments notice. Better to just take the safe route, unless you just like Drama.