Exchange year in Japan?

So as the title already suggests, I want to attend a year of high school in Japan. I’m well aware that there are many people advising against it due to the negative impact on your GPA and whatnot. The thing is, I’m starting 9th grade in a week or so, and therefore hope to spend 10th grade abroad. I have no peers or acquaintances that have done this, let alone an exchange program before so I’m kinda relying on the internet.
Now to my main concerns:

1. I don’t live in the USA but in Austria (Europe), and I have no idea if we have something remotely close to GPAs or SAT/ACTs.
   What we do have is our finals/graduating test, called the “Matura”. Although this is pretty irrelevant as I’d still have 2 years to prepare. How will the exchange year affect my marks for 10th grade? I would be willing to try and skip the year if that’s what it takes to still get straight As, but that’s more or less my last resort.

2. What JLPT level should I have to be capable of somewhat communicating? After reading countless posts and skimming subreddits I have come to a conclusion: Japanese high schoolers suck at English — Which is why I need to learn the language. I should be able to reach N3 (if I follow an inhumane basically torture-like schedule) by the time I depart. However, after scouring the internet for possible answers I’m starting to develop second thoughts about whether this will suffice for interactions aside from “Hello my name is Stupid Foreigner”.

3. What programs should I travel with?
   This is all based off the presumption that my already fragile dreams haven’t been pulverised, but are there any programs for Central European students? I’d also want to avoid host families, as one dispute would make my entire stay a nightmare.

4. What are the entrance exams like?
   Seeing as I would be enrolling during the first year of Japanese highschool, taking an entrance exam seems logical. I don’t want to rely on my Japanese proficiency and academic skills too much cause this is Asia we’re talking about. This goes without say- Asian countries are known for boasting superhuman calculators and extremely rigorous curriculums, so I’m curious as to what extent the gap between me and some Japanese kid reaches so I’ll know where to start filling the void. (Or maybe my idea of Asian kids growing up in Asian countries is just wrong)

5. Is it worth it?
   This is a rather vague question but I want a clear answer. Yes or No?
   I know the option of spending a college year abroad is there, and I have given it much thought. But I can’t ignore the fact that it’d be completely different from the Highschool experience. Besides I only get one shot at this, I can’t afford to sacrifice any other year than 10th grade without dooming my future, and it’s already too late to spend 9th grade in another country. I will never get to know Japanese Highschool and culture and whatnot if I don’t do it in 10th grade.
   Then again there’s the possibility of having to repeat a year and messing up my entire academic record, which is exactly why I’m asking you guys: is the experience worth it?

6. Will I learn anything at all?
   As a self proclaimed stupid foreigner, I don’t want to lose a year and go on what is essentially a vacation, the rest is self explanatory.

Thank you for listening to me blabbering on and on about a stupid wish and reading this nonsense! I really appreciate it!

Hopefully this will be useful to some others as well.

~ some 13 year old