It would depend on what it is you want, and what you want to use it for. I don't have a whole lot of experience with commissioned writing, which is why I don't advertise it here, but send me a note and we can discuss it
I am thinking there will be some lore that is only written and presented on the website, other narrated on trailers and such. I would need the main server lore, some short stories/fables, a few poems and songs, and such.
You may need to find someone else for the songs and poems, as that is my one weakness in writing (though I may be able to do it if you have a "skeleton" of what you want), but everything else I can certainly do, as I have experience with that type of writing from working on my own fantasy novel. I have an example of something similar to what you might be looking for here: [link] and I have others I can show you that aren't currently online.
Unfortunately, no, I don't have any real credentials yet. I only just finished my Bachelor of Arts degree a couple of months ago, and didn't have time during school to take the editing certification exams, which only take place in November. However, you can see my own writing here: [link] and I will do a sample edit for her before she has to decide anything (I need a 5 - 10 page sample of the book she wants edited, so I can determine an appropriate price. I edit that portion and send it back, and then she can decide whether or not she would like me to continue with the rest of the book, at which point we finalize the price, and both sign a contract).
For straight copy editing, the price would likely be less than that. My hourly rate is based more on short essays or novels, as the vast majority of writers I work with come to me with 20 pages or less. For a full book, I will assess the first few pages, then negotiate either a flat rate (if the book is finished) or per-page rate (if the book is unfinished) based on how much work is needed and the author's budget. For straight copy editing, I would go for something closer to $1/page, or even $0.50/page if there are very few errors (about 10 or so per page), up to $2 or $3 per page for something that has a lot of errors (nearly every sentence needing work).