The 3.8 million species you suggest is outrageous and WAAAAY OFF!!
That 3.8 probably includes bacteria, protozoa, viruses, and maybe even plants.
We also need to subtract the sea creatures: fish, amphibians and the likes.
considering how long ago it was, the number of species should have reduced to between 35,000 and 37,000 species.
Building a ship of that magnitude was unheard of until the early 1900. So how did Noah build it?
That's where God comes in: He gave Noah instructions on how to build it (genesis 6:14)
http://www.abiblestudy.com/graphics/ark.jpg
As to how the animals got there, i am clueless.
We don't know what the world looked like before the flood, so it is safe to assume that the animals walked to the ark.
Evolutionists claim that there used to be land bridges though.
As for the rest of the questions, i have no idea.
http://www.zazzle.com/znews/archives/stewie.jpg