I agree with other posts that 20-40 pages per week plus all the required skills is an extremely unreasonable and uneralistic expectation for an unpaid job, especially if there's only one artist. The artist who's working for free would certainly not be able to work full time, either because they're in education or have another full time job. It seems like the only "payment" you can offer is potential income and visibility but it can't pay the bills right now.
There is nothing inherently wrong with looking for an artist who would work for free, because there may be artists out there who are invested in your story enough to want to do that, but you'd have to adjust your quality and quantity expectations drastically.
I second the others who suggested Kickstarter or Patreon since you already have a big following with the demand. You could even adjust the number of releases per month depending how much Patreon support you get.
Good luck!