I wrote a Langcorrect post saying that I made a plan to go to Okinawa on this site, finally, I took, and I've finally bought a ticket to go there.

The clause "I wrote that I made a plan to go to Okinawa on this site" implies that Okinawa is a place on Langcorrect. You could place it after "wrote" to make it clear that "on this site" modifies "wrote" and not "go", resulting in "I wrote on this site that", but the phrase "on this site" would sound somewhat odd in this context, so I changed it to "I wrote a Langcorrect post".

I changed "I" to "I've" because you use the present perfect when talking about things that are relevant to this present (in this case, the ticket is relevant to the present because you haven't used it yet but are planning to use it in the future). https://dictionary.cambridge.org/grammar/british-grammar/present-perfect-simple-i-have-worked

I will go there with five people, but two of them are working now, so their holiday is the onlyy can only go on the weekend.

Except for those two peoplem, we can go anytime.

Two friends of mine who are working join togetherwill join us on Saturday.

I'm not entirely sure if this is what you meant.

We have decided what to do in Okinawa, but we dohaven't makde plans in detailany detailed plans.

Maybe, this trip is my last trip before studying abroad.

I want to enjoy it in the besmake the most of it.