How much to charge for freelance technical writing?

I have been propositioned. On and off for years, I have done writing for magazines and translated/edited papers for publication for one-off jobs with agreed upon prices.

I have been approached by a small but international company to be their technical writer, but on a freelance basis. He said that they would accept invoices based on an hourly rate and I would simply bill for hours worked. I like working on a per-page or word count basis, but he insists it be hourly.

I have a registered entity I bill jobs through, so I don’t have to set up anything legal and costly, but how much is having a technical writer at your beck and call, (but not an employee) worth?

Is there any extra value in that the language the documents are to be published is my native language and not the language where the company is based?