I'm still scratching my head about Noah having (at least) 2 of every species on board. Even if you were just to count insects, that would be one big boat......
If you are talking about birds, mammals, and reptiles, I beleive there are about 30,000 species worldwide alive today. Subtract from that those that are water-adapted, mix in the idea speciation occurs when one group splits into two with a loss of information in the gene pool let's estimate how many species would actually have to have been on board. Your guess is as good as mine, 10,000 maybe?
That is not an impossible number. And for every large animal there are many small ones, so that the average size might be close to a chicken. I've seen one chicken house that had that many animals in it, and one family care for four or five such houses. The reptiles can go much longer without care, one good meal can keep a snake going for months, and many animals can hibernate or estivate.
If Noah's ark is a fable, it is NOT because it the science demands it be.
Might I suggest that you check out The Genesis Flood by John Whitcomb and Henry Morris. While it's not intended to answer all questions or objections, it might answer a lot of your questions. For example the Bible does not say two of every species, it says 2 of each kind, an important difference.
There are many miraculous elements in the Flood. They cannot be explained by human reason. However, if you believe in God commanding thorugh His Word, then it is clear that He commanded the animals and they gathered and entered the ark.
There are many new roses each year "invented" by man. The DNA is already there but not expressed. The same is true of dogs. Therefore I do not have a problem with species expansion after the Flood.
More importantly we are in another era like the pre-Flood time - great technology, plenty of leisure time, and almost complete godlessness. As Jesus said, "When the Son of Man returns, will He find faith?"