Can't help you with the techie stuff at all - I can with copyright issues however...
Be very, very
careful here else you could get sued out of sight. As Colin says, so long as you're not making any money you're relatively OK (as there's no dosh to be sued for
), it's always best to ask though.
As you're making graphics too you not only will need a licence from Terry, but potentially from Paul Kidby, the Josh Kirby estate and/or the production companies who made the films and animations. If your character visuals resemble any of the professionally illustrated characters or even renditions of the actors in the films without permission then you're treading deep water even without Terry in the equation.
An example - I'm selling some T-shirt type things online for DreamWorlds using my own fan art for LotR but I'm not using any
of the portraits I've done of characters as portrayed in the film because I know Newline will be on me like a ton of bricks even though I can honestly claim that I'm non-profit making and sales will going into site-running costs and maintenance. Earlier this week I even got rapped on the knuckles for a 'text string' below this piece
with the tagline "not for the last time, Bilbo wished he had remembered to pack the jungle-strength insect repellent".
Just mentioning the name Bilbo (the words aren't even a quote from the book) and Zazzle took all my mousepad range off - 5 pieces in all, the rest of which are 'Tolkien-inspired'. The visual itself you'll notice only shows Bilbo in silhouette so I don't get Newline moaning at me for making him look like Ian Holm or accused of ripping off background art from the truly dreadful Rankin/Bass animated film of The Hobbit. The other 4 designs were re-instated with apologies as they didn't feature 'quotes' and were my sole asserted copyrighted work, but for a while I was looking at having to take down all my product ranges as those pieces were used across the entire stock for that part of the online store...
Finally - a business proposition for you!
My site features textual RP only so we're not competing with you at all (or indeed this forum), but in the New Year I'm putting up a new dedicated RP and quiz/game forum for Discworld. We have a site shop and also a 'Marketplace' for members to flog their own stuff - you'd be welcome to put up an ad in there or ask for people to come and test your product, kind of thing