Self-Introduction Self-Introduction

Or "Self Introduction"

Hi Eeveryone! Hi everyone!

Hi Eeveryone! Hi everyone!

Hi Eeveryone! Hi everyone!

Hi Eeveryone! Hi everyone!

Hi Eeveryone! Hi everyone!

I'm hHappiness from Osaka. I'm Happiness from Osaka.

I previously lived in California for five and a half years. I previously lived in California for five and a half years.

This sounds a bit awkward to me if you don't include some sort of time reference.

My English writing ability needs improving, so please correct any mistakes [if you spot them] - all feedback is appreciated! My English writing ability needs improving, so please correct any mistakes [if you spot them] - all feedback is appreciated!

My English writing ability needs improving,I can't write as well as I'd like so please correct any mistakes - all feedback is appreciated! I can't write as well as I'd like so please correct any mistakes - all feedback is appreciated!

I feel like "X-ability" isn't very common in English even though I seem to be able to get away with adding ～力 to almost anything I want in Japanese... Anyway, the original sentence was great, but saying "I can't ___ very well" or "I can't ___ as well as I'd like" I think is more natural. Since you're writing is clearly not bad, I chose the latter.

My English writing abilityskills needs improving/improvement, so please correct any mistakes - all feedback is appreciated(you find) - I'd appreciate any feedback! My English writing skills need improving/improvement, so please correct any mistakes (you find) - I'd appreciate any feedback!

Your original is fine, but this sounds more natural to me. "All feedback is appreciated" sounds rather corporate...

My English writing ability needs improving, so please correct any mistakes - all feedback is appreciated! My English needs improving, so please correct any mistakes - all feedback is appreciated!

Of course, I'm also willing to help Japanese learners as much as possible. Of course, I'm also willing to help Japanese learners as much as possible.

Of course, I'm willinghappy to help Japanese learners as much as possible. Of course, I'm happy to help Japanese learners as much as possible.

"willing to" generally means that you don't particularly want to, but you can tolerate doing so. You'd sound much friendlier if you said "I'm happy to" or "I'd be happy to."

Of course, I'm willing(more than) happy to help Japanese learners as much as possible. Of course, I'm (more than) happy to help Japanese learners.

I like to make friends from all over the world, so please add me as your friend! I like to make friends from all over the world, so please add me as your friend!

I like to make friends all over the world, so please add me as your friend! I like to make friends all over the world, so please add me as your friend!

As Harrison suggested, "FROM all over the world" is maybe more accurate here? I just want to make sure the difference is clear. "Make friends all over the world" -> Go on trips all over the world to make friends. "Make friends (who are) from all over the world" -> Have friends who are from many places.

I like to make friends all over the worldwide, so please add me as your friend! I like to make friends worldwide, so please add me!