How did Pete manage to find Goofy and Max at the Neptune Inn? He wasn't following them; he left the campground before they did, and a long time and much activity had passed between the two events.
That's simple. They just ran into each other again. Pete's route could easily have been time-consuming enough that Goofy and Max could catch up, distance-wise. Pete did find what room they were in, but that's about it.
The location Max changed the map to was not mentioned at all during his conversation with PJ that Pete overheard, so how did Pete know that Max changed the map to LA specifically?
That's easy. While we can debate over who's the better father between Pete and Goofy it's obvious that Pete is more involved in the lives of his children than Goofy is. PJ only needed to mention the Powerline concert and then Pete could piece it together easily enough from there and he probably already knows all about Powerline because he cares what his kids are into if only to keep them from being involved with things he considers a "Bad Influence." I'd be willing to bet that PJ sneaks over to Max's house to play Grand Theft Auto.
PJ didn't mention the Powerline concert either, and there's no indication he talked to his father about it beforehand, and unless he mentioned Max going there to him, which he probably didn't or Pete would have told Goofy about it sooner, the fact that such a concert was going on still wouldn't tell Pete that's where Max changed the map to.
In the sequel, what kind of class was Goofy taking where the first question on his midterm is "Briefly describe the meaning of the universe" and the second is "Calculate..."?
It's likely that "Briefly describe the meaning of the universe" was only what it seemed like to Goofy due to him not being able to focus on the test rather than it being a real question.
Watching the movie again, the test's questions change near the start of the Nightmare Sequence, and that question is new, so this explanation is probably right.
Why is PJ so panicky about Goofy going to college with them anyway?
Probably because he knows Max will be moody and cranky with his father around.
Am I the only one who finds "After Today" to be...a little school shooter-y? I could easily picture Max cocking a gun and putting it in his backpack as he says "They've been laughing since I can remember/But they're not gonna laugh anymore!" The whole song gives me a kind of weird Columbine-vibe.
You're probably just projecting your own worries and fretting onto an otherwise innocent song. Relax a little, not everyone who wants to show up the people that laughed at them is going to do so with a shotgun.
I actually agree with OP. I love that song, but it can absolutely be read as a school-shooter type. In fact, if you watch the movie with that in mind, listen to Pete's warnings about jail, and Goofy's overprotective nature... they become a lot more interesting!
I don't see it either. I can sort of hear it during the first couple of lines, (which are usually cited), but not the rest of the song (which is usually not elaborated on).
Why are Goofy, a senior, and Max, a freshman, in the same classes?
Possibly they were institution-specific gen-ed classes that Max and the others were getting out of the way early, Bradley and his classmates were falling behind on, and Goofy didn't have to take for his degree at his first college? Colleges change gen-ed requirements fairly frequently anyway, and there are definitely times when a class aimed at freshmen and sophomores will have some juniors and seniors who are still catching up on them.
How does failing one semester, then retaking it, plus three years equal a four-year degree?
How many cups of sugar does it take to get to the moon?
Three and a half.
Okay, two related questions: how does Goofy manage to pay for two university tuitions and at least one room-and-board while unemployed? Even with financial aid, scholarships, and in-state public institution discounts, university tuition isn't exactly cheap. And also, who's paying for PJ's education? Pete doesn't care about higher education, barely cares about PJ and has no qualms about exploiting him financially, and avoids most expensive transactions that don't directly result in him getting something cool.