Yes, it would be easier, but overall less of a quality test for long term survival. Sending 100 of the Ark prisoners meant getting a wide range of people(for a static space-locked station) and being able to test long term viability for most people on the Ark.

Solar radiation is a thing, and we would all be dead if we weren't inside the protective sphere of Earth. On the Ark, they were further out of this sphere(which I will not get into), and as such were exposed to greatly increased radiation levels over the course of their lives. When they reproduced, those effected by the radiation were not permitted to continue reproducing(either by force or by early death) and the resistance to radiation continued down the line. In Clarke's generation, they are able to survive high levels of radiation without ill effect. It's bad science, and probably would not work that way, but it makes sense in the show.

It was probably never brought up. Remember, they never thought 'Oh, we don't have enough ships to make it to the ground with everyone, why not bring down the Ark?' It was so outside their thought process it just never came up. Or maybe it did and they dismissed it as a viable alternative, probably thinking it would take longer than simply waiting. Which brings up another point, they had a plan: Simply wait for the radiation to disperse. They were never meant to survive on the ground, so they never thought about it. To quote Jaha: 'Ours was to be a transitional generation.'

Most of the original survivors probably led very short lives. In reality, if they were exposed to the level of radiation needed to adapt in only 97 years, all of them would have died screaming with skin sloughing off, and never had kids. Since it's a show.. It's space sciencemagic, they just evolved. It's explained away in a way that doesn't make sense in our world, but does in the show.