I had noticed a guy post a entry about his/her journaling ¶
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So I thought, should iI start a daily journaling ¶
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I will start writing every day, then choosinge an appropriate one to post onto here.

"journalling" is the activity, but the thing you create by journalling is called a "journal". Since use used "should I start a" (note the "a"), the sentence expects an actual noun, not a nominalised verb, which is why the second sentence has to be "journalling". The first sentence would be ok to use either "journalling" or "journal" however.

I don't like journaling much, but would rather write a sentence, or even a word, rather than nothing.

Because recently, I don't have much ideaof an idea of what to write.

Maybe thatis would be a opportunity to find out what do I love, what is my purpose ofin life.

I might starting Daily Journaling

I had noticed a guy posting an entry about his/hetheir journaling ¶
.¶
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So I thought, I should i start a daily journaling ¶
.¶
¶
I will start writing every day, then I will choosinge an appropriate one to post onto here.

His/her is acceptable but you can use their to be cleaner.

I don't like journaling much, but writeing a sentence, even a word, rathis better than nothing.

Because rRecently, I dohaven't haved much ideanspiration to write.

I know I changed a lot here but I think this is closer to what you wanted to say.

Maybe that would be an opportunity to find out what I do I love, and what is my purpose ofin life.

"what I love" would also work but I thought it would be interesting to keep the "do" like in the original but putting in the right order.

I mMight sStarting a Daily Journal

Alternative: I Might Be Starting a Daily Journal
This one more indicates that you are imminently starting the journal (maybe you even count this entry as part of it)

I had noticed a guysomeone post an entry about his/hertheir (daily) journaling ¶
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. So I thought, I should i (start a daily journaling ¶
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/ do that) too. I will start writing every day, then choosing an appropriate one to post onto here.

If the gender isn't important, it's more natural to say "someone" here.
"Should I" is a question, "I should" is a statement

I don't like journaling much, but I want to write a sentence, even a word, rather than nothing.

Something is missing here. An alternative would be, "...but to write a sentence, even a word, is better than nothing."

Because recently, I don't have muchany ideas on what to write.

"Ideas" are considered as countable, so use "many" instead of "much." It also needs a complement; "ideas on/about..."

Maybe that wcould be an opportunity to find out what do I love, what is my purpose of life.

I had noticed a guysomeone post a entry about his/hetheir journaling ¶
¶
¶
So I thought, I should iI start a daily journaling ¶
daily, too.¶
¶
I will start writing every day, then choosing an appropriate one to post ontoentry post here.

If you want to use "a guy" you can just use "his."

I don't like journaling much, but writeing a sentence, even a word, rathis better than nothing.

Because recently, I don't have much idea to write about.

Maybe that wouldis will be an opportunity to find out what do I love, and what is my purpose ofin life.