This is my first diary. (For small numbers, it's better to write the number out in words instead of the numeral. :) )

Thank you for you visiting and reading my message!

I will try to write my diary in English to learn.

But I can't write really difficult words and sentences.

I'm not good at English, so please correct my mistakes if you want.

So please mail me without hesitation! (What you wrote is okay, but 'hesitation' sounds more normal. :) )

This is my first diary. You should take time to write out numbers for practice.

Thank you for you visiting and reading my message!

I will try to write in my diary in English for my learning to learn.

But I can't write so difficult words and sentences.

I'm not good at English, so please correct my mistakes if you want.

So please mail me without reserve!　（This works, but "mail" implies 普通郵便or航空便, so "message" would be better if you mean the internal メール）

Thank you for you visiting my journal and reading my entry!

I cannot write difficult words or sentences in English yet. - "Yet" means someday you want to have the skill to write difficult sentences.

I want to make a lot of friends around the world. - Sounds more natural this way in American English.

Please feel free to email me.