Permeability of air is larger than that of vacuum. With a ratio of 1.00000037. So force in your experiment on earth will be this much stronger just because of air as a medium.
If you would ask an outside observer, he would also notice the time dilation due to Earth's gravitation well, it will make exprtiment run a bit slower, 1-(7e-10). Same effect for the Sun and Milky Way, but im not sure how to calculate it.
You could also account for Earth's motion, it would make the experiment a bit slower, by 1-(1e-12) for spinning, 1-(5e-9) for orbital motion around the sun and 1-(3e-7) for its motion around the Milky Way
If your magnets will be really, really strong, you would create matter, that would create gravitational force in return. You probably wont be able to get such magnetic field.
But you dont even need that strong of a field in order to affect gravity. Since energy and matter are not that different, adding more energy into your magnetic field will already create more gravitational force. A bit. A Hiroshima's nuke worth of energy would add gravitational force the same as would 7 grams. So if you can measure gravitational force of your energy, you either have very good measuring tools, or you should be really really careful.
1-(4e-3) means "1 minus 4 with 3 leading zeros: 1-0.004, or 0.996". Lazy way to write long numbers. Scientists use it, but we can use it too. 7e4 would mean 7 with 4 zeros after it, 70000.
If you wanted to make a flying skateboard with fridge magnets, then no, it wont work. Even if YouTube shows otherwise.