The most common problem was finding the calmest place on Earth.
Pictures below are basic balloon chains.
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As you go higher the pressure decreases which means that the density of both the air and the lifting gas goes down.
That means that the higher you want to go the bigger the balloon you need for a given lifting force. Eventually you reach a point where it is not not practical to make the structure light enough to go any higher. The highest altitude reached by a balloon is considerably lower than the lowest altitude at which orbit is practical.
It also means that as you go higher the wind-area of your balloon increases which will put more force on the tether. The loading from the tether, both from it's weight and from winds at various altitudes will further reduce the practical maximum altitude compared to a free floating balloon.
There is also the issue that in low orbit you need a considerable sideways movement relative to the ground. Most of the delta-v in a launch rocket is spent on gaining the sideways velocity, not in gaining the altitude.
No, it would not work because there will be a point where the balloons will stop rising due to the fact that the density of the gas inside and outside are the same. In space, you have a near-vacuum which is lower than the density of the hydrogen inside the balloon which means that you cannot have a balloon floating in space.This short article talks about helium balloons, but the principles are the same (The numbers for hydrogen should be different though, but not by too much).