Well not everything would need to float at earth pressure. The production of any fuels or materials that required heavier equipment could be done at lower atmosphere. You could engineer bacteria to break down sulfuric acid for the hydrogen based fuels, obviously the CO2 to O2 part would be easy, or bacteria to produce certain materials. Also I wasn't talking about methane fuel which would need nuclear I was thinking more basic hydrogen rockets which chemical reactions could be simple and effective enough to produce. Additionally solar is already getting thinner and lighter so I don't think that would be much of a problem. And remember on Venus it's not just CO2 it's very dense and high pressure as well. So earth atmospheric pressure air could lift quite a bit and you don't need to be at exactly sea level pressure all the time. Only real problem I see other than the constant threat of death that all colonies will face is launching to and from any floating colonies.
As for the large blimp colonies, I see nothing wrong with that. Sure they'll be big but not any more difficult than building reinforced lava tube colonies on the moon or going to Mars with building sized 3d printers or excavators that can be used to make long term shelters. Like I said all of the planets are going to have tough problems, short of an earth like planet you aren't going to find an ideal easy scenario. Personaly giant airships housing 50 or so people doesn't seem too bad. Like I said though it's the landing and taking off that seems a bit trickier.