If your aircraft cariers ect have an average density of more than one kilogram per cubic meter = 1/1000 th the density of water, they will float below the cloud tops of Venus where the sulpheric acid clouds are found, and little solar energy is available. CNT = carbon nano tubes may permit a low enough average density to stay just above the cloud tops which I agree is ideal, except the habitats will fall if large quantities of carbon dioxide leak in. I agree linking them (with air locks) makes falling very improbable as it is very unlikely more than one would have a bad leak. Floating cities high in Earth's atmosphere have much the same problem, except the inhabitants might survive the fall of their habitat to Earth's surface.
I posted something similar on another thread. You could build cloud nine structures on venus (
http://stevendejonckheere.blogspot.com/2006/08/cloud-nine.html). These could be made into 2-part domes with one section providing lift and one made for habitation. The main section could be lower pressure and heated by solar panels. The atmosphere might be a combination of oxygen, nitrogen and helium. CNT materials would enable you to get more bouyancy. We may eventually have a large number of these structures and use ceramic balloons to ferry robotic miners and ores up and down from the surface. We could also harvest the sulfuric acid and the CO2.