Venus: If you want to colonize an atmosphere why not do it on Earth? I see absolutely no reason to think this is viable. You certainly have no access to the heavy elements.

Apply the key question. DO YOU HAVE ACCESS TO ALL THE RESOURCES NEEDED FOR A SELF SUPPORTING CIVILIZATION? Answer no way.

As far as "why do we need a solid surface?" - are you planning on colonizing without factories? Industrial factories are massive. You plan on adding another ridiculous cost factor by requiring massive additions in equipment and support structures to make them float? Venus is an absolutely nonsensical suggestion for near term colonization. Venus requires terraforming or amazing new technologies to be a viable option.

Moon: How does regular trips back to Earth cancel low gravity and lack of resources? These trips are extremely expensive. The whole reason for focusing on resources is to minimize the cost of colonization to make it financially practical. Even Mars is a big stretch at the moment, everything else is 10, 100, or even a 1000 times harder.

Apply the key question. DO YOU HAVE ACCESS TO ALL THE RESOURCES NEEDED FOR A SELF SUPPORTING CIVILIZATION? Answer no.

Mars: It is not very low gravity. It is 0.38g, almost half of Earth's and more than double the Moon's. We currently have no idea whether this means low g effects will be negligible, plateau off or be continuous downward trend at a slower rate than 0 g. The Mars Biogravity Satellite project hopes to address this.

Apply the key question. DO YOU HAVE ACCESS TO ALL THE RESOURCES NEEDED FOR A SELF SUPPORTING CIVILIZATION? Answer YES.

As for your time issue you seem to be totally ignoring colonization and exploration history. 6 month trips are shorter than many trade and exploration journeys by sailing ship. They are also comparable to the total length of journeys made to colonize America. The value of the destination matters far more than the time to reach it. It's a matter of elementary economics. If you can't live somewhere or make a living there you won't journey there other than as a tourist no matter what the distance is.

Regards,
Mark