Is it possible for me to get into a good school with bad freshman year grades?

"Stanford and the University of California system are perfect examples of appropriately evaluating prospective students. They do not count freshman grades at all in admissions decisions, and instead recalculate applicants' grade-point averages without them."

So, yes. It is very possible for you to do get into a "good school" with "bad" Freshman year grades. I know you probably meant T20 or T50 schools, but keep in mind there's plenty of good schools that will admit students to a lower standard compared to Ivy Leagues and T20's, that also provide the same quality of education and opportunities. Also, your GPA is stellar at the moment. It will serve as an excellent foundation for you throughout high school and hopefully will allow you to take more rigorous classes if you feel you're ready.

Answers to your questions:

It's important to challenge yourself academically. The standard to which you do so fluctuates a lot depending on who you ask, with some recommending to take the hardest classes you literally can, and others recommending to take the hardest classes that you can manage. I would personally follow that. There's times in life where less can be more if the execution is better, and I believe this is one of those times. You'll maintain a better GPA and better extracurriculars with the time given from taking less, but challenging classes such as AP, IGSBE, Duel Enrollment, Honors, Pre-AP, etc. However, make sure to take the classes you're interested in too! It's a good idea to theme your selection in a way to show your passion for these subjects, or a grand subject. The idea of a theme within your application is very important for top schools.

Performing well in these classes is different for everyone so I can't really recommend a specific way to do well in them, but just keep in mind your method of doing well might be different from someone else's and that's okay. Usually a good idea though while studying is to actively learn rather than passively. Practices and such related to these I believe would be explained better and easily with a quick google search related to the subject.

I honestly wouldn't even start preparing for the SAT / ACT until you've taken the PSAT or pre-ACT, if they have something like that, at your school. This way you know what to improve and you'll learn most concepts to begin actually studying for the SAT / ACT during your late sophomore year and beyond. For this reason, I won't really get into this subject.

There's plenty of people who performed poorly their Freshman year but were able to get into good schools. It's really just a trial year for you to explore your interest and get a taste of high school. Just keep pursing what you're interested in and gradually increase the significance and your involvement into these interest. Best of luck. You seem to be doing very well considering the things you mentioned having, so please try to give yourself some credit.