My understanding is that the bed bug issue is relatively contained at the moment. Nonetheless, the last CVW they took all the drags that were assigned to companies with bed bugs and placed then in ones that did not have any bed bugs, so your son/daughter should be fine in that regard.
As for the mice, they are, and probably always will be, in Bancroft. As long as you put whatever food you have in a plastic container, they won't get to it.
Now for the questions:
18 MIDN hit most of them, but I'll give some more input
The hardest part of the application process for me was the medical part because I had a medical condition and for a while I was not sure if it was going to be waived or not.
I came in wanting to do Marine Corps Aviation, but now I'm not so sure. One of the positives of USNA over the other SAs is that there is a wider variety of things you can do after graduation, so it's a good place to go if you know you want to serve in the military as an officer but aren't quite sure exactly what you want to do specifically.
The academic year pretty tough from a time management standpoint. Living in Bancroft can get stressful because you have a whole bunch of upperclass monitoring you and disciplining you when you screw something up. There is not a ton of privacy and the days are pretty long. It could be worse though.