J-language school & immigration office

Hello all. I am 22 years old from Greece. I want to learn Japanese in a Japanese language school, thinking for a two-year course, as I have not attended to any Japanese institute or school class in my country, and after graduating from there going to a university or college in Japan. My knowledge is very limited, up to a few words and random phrases as well as some hiragana/katakana, which I learned by myself with the help of Japanese learning books. I have graduated from high school (12 years education) and attended to a college here in my country, but it isn't what I am seeking and with my affection in Japan's the culture, history, technology and arts, I decided to go there and study instead staying here and doing something that would not satisfy me. I am determined to succeed this time in a country that I love and admire. After this short prologue I would like to ask some questions.

As a high school graduate and without having any official certificate in Japanese language, will I be able to enroll in a Japanese language school or the immigration office will turn down my application? I have the impression that immigration requires the qualification of Japanese knowledge like JLPT or J-test for high school graduate students like me.

Also I would like to know if the graduating marks of the high school are of any importance or only that you have graduated from high school is what matters for the immigration office.

Finally, as I learned recently the pre-college student visa has been canceled and there is only college student visa. In my knowledge college visa is valid for two years. If I use my college visa to study for two years in a Japanese language school will I be able to study further in a university or college with college student visa again?

Sorry for the length and the many questions. I would really appreciate any help.
Thanks and regards.

No you do not require Japanese language proficiency to go to Japanese language school. I have met a few high school graduates who were in Japan to study Japanese, you should be ok with immigration as long as you are:
1. Admitted to a Japanese language school
2. prove you have financial support

- I have not heard that they terminated "precollege student" status. This one is for one year or for six months, which can be extended as you continue your language study. Normally you look for a language school first, inquire, apply with the school, and after you've been accepted and paid in the tuition, the school on your behalf applies for the visa so that you can come and study.

- If you want to continue then to study at a university in Japan, (of course you need to be accepted by the university, but in terms of visa) you will need to change your status from "precollege" to "college" student status, which can be done while staying in Japan if you have the necessary documents/funds ready.

Thank you very much for your answers. You made my day :p, I am in your debt.