On the margin I think its usually better to take less and/or easier courses. It is better to do very well on an easier schedule than do "ok" on a hard schedule.

I was uncertain, coming from high school to university, whether or not I would adjust well. So I did the cautious thing and hedged: I only took 12 credit hours (the minimum load) the first semester.

About three weeks in I was talking to one of my professors, complaining that I was bored out of my mind. They offered me a research position in their lab, and getting involved in student research my first semester was much more helpful than a class would have been. Similarly, if you find yourself with spare time and energy, find a productive outlet for it. Get used to building in pad time for yourself and then using that pad time flexibly. (This is a key factor in avoiding burnout during your adult life, I think.)

If you apply for a job or grad school everyone will look at your gpa.

That, I think, is false (though universities encourage the undergrads to believe this). Employers don't care about GPA at all.

This is one of those "depends" pieces of advice. At some schools, the entire Freshman year GPA is completely forgiven, ignored, or given specific exemptions in how it's factored into the final GPA. In this case, why not go for broke? I always suggest starting out with the hardest thing and then ratcheting down instead of vice versa.

In reality, I think people usually underestimate themselves. It's better to try the hardest possible path and then find your limits, than be cautious and never discover them.

As a professor looking for promising graduate students, I don't care about GPA very much. Well, I suppose a super low GPA is a signal (but even then does not rule you out).

Admission committee might care.

In many programs you may also be able to take fewer classes during the full semesters and take fluff classes over the summer semester. If your program requires, for example, music appreciation or a physical ed class, these are good summer class; they are easy, you don't loose much by having the class shortened/modified, and they aren't distracting you when you need your attention for more important classes.

If you apply for a job or grad school everyone will look at your gpa.

This might be cultural/regional; in Finland it's common for employers to not care about grades, just whether or not you have a degree. (Though grad school will definitely care about the grades.)