I am currently a sophomore in high school and I’m stressing about what classes to take next year. The only options for some classes are AP instead of honors, and I’m nervous that I won’t be able to have a good GPA if I take some of those classes. So far I have taken all honors and have a 4.2. I’m considering doing all regular next year, but really just want to know if colleges really care about honors and AP as long as I have a 4.0 in regular from here on out.
It depends where you want to go to college. There are hundreds of colleges that will want you with ‘regular’. If you are looking for highly selective colleges, though, they will care (they typically say that they want both AP/honors + top marks). For them, it’s about you showing that you are somebody who pushes themselves, that you are able for more advanced work, and that you have the self-discipline and study skills to manage it.
Talk to your parents / teachers / GCs: see if this just a crisis of confidence, or if you are right that you are best placed right where you are.
Definitely don’t drop from all honors to reg. Any decrease in course rigor will be looked negatively upon. Also yes, an A- (or even B+) in an AP is much better than an A in reg. Not taking honors/AP tells colleges you are unwilling to take advantage of your resources.
If you have excellent grades in the Honors classes, you probably will do just fine in the AP classes. Since you have specific concerns about specific classes, speak with the teachers. Ask them if they believe you are ready. I expect that they will tell you you are 
If there are just regular and AP classes, then AP is effectively the honors track. If you’re done well in the honors classes on the honors track to date, AP courses would be the next logical step.
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Absolutely. Course rigor is one of the top factors looked at by college admissions officers. It’s pretty much tied with “Grades in all courses” if you look at the survey results at https://www.nacacnet.org/globalassets/documents/publications/research/soca_chapter3.pdf
That doesn’t mean you have to take AP courses. But the strength of that component of your application to colleges will be weaker. There are certainly schools that accept students with “regular” schedules. That’s probably the majority of schedules. But more selective schools will expect more rigorous coursework.
Discuss it with your teachers - they know your capabilities and the demands of the classes.
I would suggest you take a mix of APs and honors courses. Academic rigor is a big component of college admissions at selective colleges. I think it can sometime compensate for average test scores as long as you have a good GPA.