You need to pay attention when you watch a movie mate. Cooper was the one that was trained for the mission before he chrashed but he didn't know it. It was explained in the movie. That's the reason why he could fly the ranger.

For one thing, the whole premise is that there's a disease that's keeping crops from growing

Yea, an extremely powerful disease that they could not possibly defeat with in there current state. A disease that killed all the crops and took away the oxygen in the air. Oxygen and food are pretty serious stuff when it comes to survivel.

McConaughey had to have the wormhole explained to him on his way to the wormhole!

He was a pilot mate. Not a scientist. This was explained multiple times in the movie. (also a bit painful obvious explanation for the audience)

Finally, not even going into the logistics of the tesseract, how did McConaughey survive entering the black hole, and how did he manage to get out of it by the end of the movie?

If the black hole is super massive, which this one was you can in fact survive falling through the event horizon into the black hole since the gravitatonal forces are so weak there. Then we have no clue what is going on inside a black hole so you can't possibley be realistic there. This gave them the opurtionity to do whatever they wanted which in this case, Cooper ended up in a 5th dimensional space. And in the 5th dimension gravity is believed to be an dimension.

The only thing that they streched the scientific was the fact that the spaceships could escape the gravity from the black hole. You would literally have to go more than 50% of the light of speed to do that. Overall it was very scientificly accurate. You should read the book about the science about interstellar if you're interested.