Making Plans: More thoughts on #illustration and #crowdfunding

(This is a follow-up to my previous post.)

I've been reading haikujaguar 's excellent blog posts on business practices for artists, which have been both informative and encouraging as I continue to study my options.  My answers to the questions from  this post in particular lead me to believe that I'm on the right track with my idea to solicit contributions from writers:
( Click for said questions, and TL;DR thought process )

What I'd like to do is invite the storytellers out there to submit short scene descriptions or story excerpts that I can use for quick sketches and experiments. I hope to attract weblit and otherwise self-published authors to this project, but anyone with a story they'd like a picture for is welcome to participate.

Art from this project will be released free for non-commercial sharing under a creative commons license, so payment will be optional for those who are happy to use the rough sketches as-is. Contributing writers can send me tips in exchange for making revisions, or doing any more work on the images. If the author is willing, their fans will also be able to donate toward illustrations of the stories they enjoy. Licensing fees can be negotiated for anyone who wants to use my work commercially, eg. as part of a book they plan to sell.

My personal objectives are to increase my productivity and to grow as an artist by drawing things I wouldn't have considered on my own. Every sketch is an opportunity to practice and learn; feedback is important to me, so I'll post each sketch to LJ for comments, and maybe link to the comment thread when I add the image to my gallery.

A few details still to work out: 
Pricing. I like the "pay what you think it's worth, adjusted for what you can afford" pricing model for personal commissions, but I wonder if there should be minimum thresholds for 'finished sketch', 'full painting', etc., especially if several people are sponsoring the same illustration. If this project becomes popular, I won't have time to turn every sketch into a finished painting, so having a way to control the demand might not be a bad idea.

Feedback incentives. I appreciate constructive comments, and I'd like to find a way to reward people who consistently make helpful posts, to let them know their contribution is valued. What would be the best way to approach this?

Anything else I might be missing?