#16 Most of us are born with the five senses to detect our surroundings, which we're provided with.
#17 What/who knew that had Earth been set nearer to the sun, we would burn up?
#18 What/who knew that had Earth been set any further from the sun, we would freeze up?
#19 What/who knew that had Earth been built larger or smaller, its atmosphere would be one where it would not be possible for us to breathe?
#20 What/who knew that we require the oxygen of plants, just as plants require the carbon dioxide of us?
These really are all interesting questions, except for the obvious implication in the phrasing of the last four. These are all misapplications of the Anthropic Principle. Let me address each "proof" on the facts first and then address them all as a group.
With respect to #16, I would really like to ask our dear theist just why it is that five senses is somehow ideal. There is a ton of information out there that's available about our surroundings that we simply can't experience without technology. Bees sees ultraviolent radiation that we can't see. Why not? What about infrared? Why can't we just stick out our hands (which already sense heat in a rudimentary fashion) and "see" the heat signatures of the objects around us the way that night vision does? And why can't we see in the dark as well as cats? Don't we need to defend ourselves from nighttime predators? And what about our sense of smell? Why isn't it as good as a dog's? Or what about our hearing? Why can't we do echolocation just like bats or whales? Or what about sensing magnetic fields? Birds seem to navigate by sensing the Earth's magnetic field, why can't we? Or why can't we do even better? Why do we lose the senses we do have as we get older?
I could go on like that for a while, but I trust I've made my point. The five senses we have work okay, and we get enough information to get by, but the collection of them can hardly be said to be perfect. And there is plenty out there that we can't detect. It doesn't cease to be important because it isn't obvious to us. Ultraviolent is quite important to bees because they can see it. We should not be biased by our own perspective here. If we had three, six or eight senses, we would assume that they were somehow perfect and the rest superfluous as well.
We can address #17 and #18 together. While it's true that Earth is in what astronomers refer to as a habitable zone, it's not true to say that where we are is somehow perfect, in a Goldilocks kind of way. If we were closer to the sun, we would require less carbon dioxide to stay warm. If we were farther away, we would need a little more. Humans are also perfectly capable of adapting to a range of temperature conditions, as are plants. The current temperature range is hardly "ideal" in any real way either. And since we don't know exactly what set off Venus' runaway greenhouse effect, it's not to say that Earth at that location would necessarily have done the same thing, and likewise for Mars. Earth is larger, and at the location of Mars, we would certainly have an easier time hanging onto an atmosphere.
Which brings us to #19: there is absolutely no evidence for the claim inherent in this question. The atmosphere would hardly be toxic if it were thinner, or thicker. The fact that Mars and Venus are both predominantly CO2 is no reason to think that Earth at those positions would have evolved identically. And if life had evolved on such a planet, whatever life evolved there would have evolved to survive in the conditions that were present, or they would have died off.
As for #20, plants were here before us. CO2 was here before us. Plants evolved and emitted oxygen, and only after there was enough free oxygen could animals evolve to utilize it. The balance is maintained because if the plants died off, so would we. It's a very basic dynamical system.
Having addressed these all individually, the basic problem with all of them is that the theist is putting the cart before the horse. The theist is assuming that someone had humans specifically in mind when designing the Earth and therefore set the Earth up to service our particular needs in our current configuration. This is not, however, how things really came to be. Rather, the Earth evolved into it's present configuration and life, and subsequently humans, evolved up into the environment available to us. If there were a different environment, we would have evolved differently, perhaps into something entirely unrecognizable. And frankly, even with the Earth reset to into original configuration and let the "program" rerun, there is no guarantee we would evolve again... indeed, it's highly unlikely.
In summary: the world is not suited to us... we are suited to it.