Why do you have to take English classes in high school?
To be able to speak the language articulately and to be able to use grammer properly. You don't want to appear ignorant, do you?
English classes in Middle School and especially High School are the biggest waste of time. Taxes shouldn't pay English teachers money to read books to us. Nations are far ahead of the United States when learning foreign languages because of this! English should certainly be removed from the curriculum because students start learning English grammar as early as elementary school!
That depends on what classes you take. Generally, however, high school will be much harder. If you continue to take the classes you should take (i.e. you take classes in the high achiever program in middle school and then take honors and AP classes in high school), then yes, high school will easily be more challenging. If you take high achiever classes in middle school and then take general classes in high school, then middle…
English, chemistry, biology, maybe physics. High school classes have practically no bearing on your graduate studies. All you need to take in high school are the requisites for admission into a university of your choice, and from there one would have to take courses required for your bachelor's degree, and admission into medical school.
Your classes in high school should be geared towards fulfilling the educational requirements of your school and exposing yourself to a variety of topics in preparation for the general education requirements you will have to fulfill in most colleges. Writing/English and any communications classes you are able to take will of course be beneficial.