Hello. I was living in Japan for 6 years. I graduated Kokushikan University so like you I had an experiece going to Japan to study. I 100% understand what you feel. Don't worry it's easier than you think. Japanese will be super helpful if you have any problems. But making friends...Well... I can say that about 95% of all japanese studens do アルバイト and they simply don't have time to hang out with you. In my first year in Japan I had friends from all over the world but unfortunately not Japanese friends. Just don't be upset when they never call you back even if they have promised. It's not because they don't like you. You just need to consider that they have obsolutely different culture and mentality. But I'm sure that you'll find friends if you want to. I finaly did. 

Good luck with your留学！頑張ってね。

I studied abroad in japan for a year too, though it was in a highschool and not a university. My regret was not actively introducing myself to my schoolmates; they were very interested in me for the first week, but I was too shy then, and later realized I had missed many oppourtunities to make friends. 

It may have been because I was in highschool, but i was often approached for help with english homework, and everyone was happy to help me with practicing japanese. So I don't think you should be too worried about only meeting english speakers. But do introduce yourself nd have fun.

Hello, I understand your anxiety、But your Japanese is not bad haha. Japanese students are shy but they are very friendly. Do not be afraid to go ahead and talk to them in Japanese, they will be happy to learn about you. However, most of the Japanese students does not speak English, or too shy to talk in English. So I recommend you to talk in Japanese most of the time, it is also very good for your goals right? :) 
I want to go to a Japanese langage school for a year I envy you so much haha!