You left out the room needed for food for forty days and nights. Plus, many animals were supposed to have been taken in greater quantities than just two per species. There was also a wee logistical problem of gathering up all those species from around the globe, much of which had not been discovered and/or was not accessible. Would have required one heck of an aquarium . . . well, actually two aquariums (one salt water, one fresh) somewhere.
Now, while I don't know about any "shittim" wood and won't pull out the ol' "miracle" card, I would guess that it would have surely taken something akin to a miracle to dispose of all that animal, insect and human "shittum". Good thing there was only a couple of flies from each species, huh? But surely could have used a few extra dung beetles . . .
Hey - what about all the critters that ate or damaged wood?