I think it is important that he knows what level of Japanese you are at if you are going to do an exchange. If you can't read the message you should just tell him instead of getting other people to translate it for you.
You want to learn right? ^^ If he knows your level he can write stuff at a similar level and you can learn from that right? Instead of struggling through lots of Japanese that you don't really understand properly.
Anyway this part of what he said is important, he wants you to choose what you want him to do:
■あなたは、自分の書いた文章が少しでも不自然だったら、それを指摘して欲しいですか?
Do you want me to point out if what you wrote in Japanese is not natural? (He will put what you wrote into more natural Japanese, this seems like the good option)
それとも、少しぐらい不自然でも言いたいことが伝わるのならそれでよいが、内容が分かりにくい、または誤解を招くような表現だと私が思ったときだけ指摘して欲しいと思いますか?
Or, do you want me to just leave it even if what you say is not natural but the meaning is understood? And then only correct what you wrote if I think there could be a misunderstanding/miscommunication?
I think the first option is best for learning. Under that he corrected one of your Japanese sentences for you.
Good luck.
Edit:
Um, did you read my reply?
You wrote: When my writing is even slightly strange, I want you to point it out. (But, why is there a question mark? Do I have this part wrong?)
I already translated this for you, he is asking YOU if he should correct YOUR Japanese if you write something strange.
You wrote: (These next two lines, no clue....)
I translated this above already. (^^)'
Anyway, good luck. Maybe someone else will correct the rest of your translation, I don't have time now... some of it is wrong btw. If other people translate everything for you then he is going to think to himself, "oh, she can understand this", and then will continue to write to you at the same level of Japanese, and then you will have to get other people to translate everything for you all the time... doesn't make any sense right? ^^