Your habitat won't float as well once I transport some asteroid-mined calcium and magnesium to Jupiter, turn it all into hydrides, package it with transition-metallic catalysts (Co, Ni, Fe, Ru), and shoot it into Venus.
MgH2 -> Mg + H2 (thermolysis @ 287 degC)
CO2 + H2 --Fe-> CO + H2O (water-gas shift)
CO + H2 --Fe-> C + H2O (Bosch)
CO2 + 4 H2 --Ni-> CH4 + 2 H2O (Sabatier)
2n+1 H2 + n CO --metal--> CnH(2n+2) + n H2O (Fischer-Tropsch)
2 Mg + CO2 -> 2 MgO + C
CaH2 + 2 H2O -> Ca(OH)2 + 2 H2
Ca(OH)2 + CO2 -> CaCO3 + H2O
We might have to switch to double-hulls, with the outer section filled with hydrogen. That would be concerning in an atmosphere with appreciable free oxygen, but I suppose you have a plan for that.
The chemical intervention is only sufficient to get the excess of CO2 out of the atmosphere, which would get the surface pressure down to maybe 3 bar of mostly N2. From there, we'd still have to cool the atmosphere down far enough to support thermophilic autotrophic microbes in the new surface lakes. They would produce oxygen, but slowly, so there wouldn't be any appreciable free oxygen available for a long time.
The primary concern would be that Earth-gas would not be a good enough lifting gas in the CO2-depleted Venus atmosphere to keep the floating habitat at a cool enough altitude. Hydrogen-filled chambers would certainly work for that, but you would have to bring that hydrogen with you to Venus. By the time atmospheric oxygen becomes a risk, you would just land the dirigible and burn the hydrogen in a controlled fashion.
Because that would involve bringing along a reactive metal, bringing one H2 molecule with you is less mass than any of the metal atoms that would react with H2SO4 to give you the same amount of hydrogen. But perhaps more difficult to handle as a gas.
You could bring along MgH2, then once you hit the atmosphere, you can thermally decompose it into Mg and H2, then react the Mg with sulfuric acid to get MgSO4 and another H2.
