I feel in a decent position to offer a bit of advice, but I only just finished my first semester in university in a Double Honours Astrophysics and Pure Mathematics program, I took:
Calculus I, Honours Math: Proofs in Set Theory & Number Theory, Logic I: First-Order Logic, Introduction to General Chemistry, and Honours Physics: Classical Mechanics I.
I also almost didn't get an A in my chemistry class and I really pulled myself together at the end of the semester in Honours Math (spent around 40 hours studying with others from the class before the final, so I got 100% on it after receiving 84% on the midterm).
My main problem near the middle of the semester was that I was doing too much extracurricular reading and had committed to too much. I was reading through a graduate level convex geometry textbook, chapters from Rudin's Real Analysis, and trying to have friends, and oh wait- "That logic assignment that takes 15 hours is due on Friday... It's Thursday morning". I'm not sure if this is what a lot of people who are academically oriented do, but I would strongly recommend against it. You can study whatever extra stuff you want over breaks, and not during the semester, focus on the actual classes you have.
As for studying:
Chemistry: I probably studied an hour a week, I'm really surprised I pulled off an A, I pulled the "cram before the final exam" and it worked out well. I'm sure this would be the ONLY class that it would be possible to do that for.
Calculus I: I did the weekly assignments which I ripped off in about in an hour or two and didn't do anything else, this was because I did calculus in high school.
Logic I: A ridiculously time-consuming class, with assignments that were so massive you would literally have to spend a full day to finish them. I didn't really have a chance to "study" for the class outside of working on assignments for it, I probably spent 15 hours a week outside of class on this class.
Physics: I thought I was ahead in physics because I attended a summer program and "I knew my stuff", but I sure as hell got a wake up call when I got 80% on the midterm, so I studied really hard (probably 2-3 hours a day every day of the week) during the second half of the semester to make up for it. Remember to stay at or ahead of where the class is at. You know that if the class is lecturing a day ahead of where you are at in the material that you need to not talk to anyone, head to the library and catch up immediately.
Honours Math: I probably spent more time on that class, than all of the others combined. Probably 20-30 hours outside of class each week working on really challenging assignments with a study group (one of them took 20 hours over 2 days), attempting every single question in the textbook, reading over notes from the lectures, and trying to make up my own questions and solve them to gain some intuition and creativity for proofs. For me, the course was extremely challenging and difficult, but I LOVED IT. I feel so much more mathematically mature, and it really has helped me develop a passion for mathematics.
Overall, in the first part of the year (before Midterms) I spent around 20 hours outside of class, hung out with friends twice or three times a week and was studying a lot of extracurricular books in my free time. After getting my midterms back and seeing that I was heading for the B+ to A- range, I decided to get my act together, put away my graph theory and convex geometry books and let my friends know that I'd see them over the winter break. I probably spent about 50 hours outside of class studying for the second half of the semester and it paid off. I got 100% on my Honours Math, Logic, and Physics final exams, and got an A on Calculus and Chem.
Hopefully that is helpful to let you know how hard it is for someone with a decent level of intelligence to get a 4.0, but I'm sure next semester will not be as bad since I have learned a lot about prioritizing and studying efficiently.
Remember that social interactions and having friends are important! You need to take a break for a while, and I'm fairly convinced that time spent studying is in an inverse square relationship with how effective that time spent is. If you can spend 3 hours studying, then go for a run, come back and spend another 2 hours studying, then play a game of chess with your roommate/friend and play guitar/piano for a bit, then head back to the library/your room to study for another 3 hours, that will be WAY more productive than spending 9 hours straight studying and being burnt out for the last 4. Not to mention, you will enjoy your life more!