My bid is simbolic as I am not quite certain at the moment what exactly is included in this project. What I mean is that, in the first paragraph, you mention that the writer will be responsible for more than what you mention later, ie. the quest system, while later there is mention of only descriptions, tutorials etc. and word count. I have done this type of work before on a game called 2moons, but have also written an indepth tutorial for the MMO The Secret World, which ended up being 90 pages or 50k words long. You can find it by searching my name on the killerguides page.
We will have to talk a bit more in depth about what exactly you want from a writer on this project and I hope we get a chance to do that, as I would love to work with you on this.
As I understood it, you need someone to also write the text for the quests, but as you said "quest system" I also presume you may mean more than that...
Anyway, hope to hear from you soon!