Yes, but I tend to limit the amount of pages. Between 10 and 15 is fine for a standard project, maybe 20 if I like the concept myself. My problem with Doujin is they take a while to do, so I have to suspend excepting all other commissions until complete.
The rate is the same as any other image, but every page will be very high quality colour pages. I don't do that first 3 pages colour then screentones the rest. Firstly, I find it difficult doing screentones digitally because you need to work 1:1 scale or you end up with a page of greys. I usually work 30:1 at the very least, you image will probably be the size of your front door if a little smaller in hi resolution. I'll also supply normal sized versions.
Secondly, you must pay upfront for each page. If you choose to stop the doujin half complete, I won't refund the cash for any previous completed pages you've recieved. That's a no-brainer.
Any questions though, feel free to ask.