"If Earth was on fire after the Big Bang, how did the first cell develop in such harsh conditions?"

The first cell didn't developer until millions of years after the earth cooled.

"Did humans crawl out of a swamp? How did we evolve from a water-based organism?"

No. Simply put, the fish-like creatures that could drag themselves over land from one body of water to another had an advantage over those that couldn't. Over millions of years small advantages add up to larger advantages. First, it's the ones that can drag themselves a few feet. Then once most of the ones that can't drag themselves a few feet are dead, and the ancestors of the ones that could are still alive the "competition" becomes which one can drag themselves further, and faster. Then it's which ones have gills that can manage to wrangle a tiny bit of oxygen out of the air as it pulls itself across land that win. Then their ancestors that can pull the most oxygen out of the air win. etc, etc, etc. Just look at what we've done to dogs through unnatural selection over the course of a few hundred years... now imagine we kept doing that for millions of years.

"If everything started off from a Big Bang, how is Earth in mathematically perfect distance away from the Sun that allows survivable conditions for all living things?"

Because the living things on earth are here precisely because of those conditions. You're looking at it exactly backwards. Out the trillions and trillions of worlds, this one has good conditions for life. The really extraordinary thing is that the very large majority of planets aren't the "mathematically perfect distance."

"Is it all just a coincidence that there is no other place like Earth in rest of the Milky Way galaxy as far as humans know?"

Yes.

"Why is a human body such a perfect creation with no flaws--from toes to brains?"

It's not. We get sick, we die, we have appendixes, tonsils, and wisdom teeth that often have to been cut out, etc.

"Why do humans have conscience from what is wrong and what is right?"

Because we developed empathy over time because it helps preserve the pack.

"Everything is so perfect, it can not all be just a coincidence. There must be a higher power (God or aliens) at work."

Go spend a day or two in space, which makes up 99.9999999....% of the universe, and tell me again how "perfect" everything is.