Answers:
1) Zero
2) No
3) Zero
1) The payload on the big balloons weighs over a ton.
2) Both the small and large balloons have electronic systems; smaller ones simply run off pre-charged li battery, larger runs have substantial solar charging capability (kilowatts)
3) The balloons are not in orbit. Gravitational force is proportional to mass. Weight is non-zero.
The figure given for weight of water is wrong.