Your mod looks like a very good idea, especially for starting characters with a low alchemy skill. Your scroll images would definitely benefit from using alpha channels though, to remove the blank background.
I've been working with .dds files for a while now, using the dds plugin for photoshop. I find it very reliable (just remember to flatten your images before saving to avoid the occasional "too many channels" error message). I don't know if there's a similar plugin for Gimp, but there probably is one out there. I find that dds dxt3 with no mipmaps (that's the dds type with explicit alpha) works best for book art (particularly line art). It gives nice crisp images, as Illuminiel mentioned, which is perfect for detailed line art. I've converted all my old .tga files to .dds and I'm never looking back.
This is an example of using an alpha channel to best effect when using a simple line drawing (works with either .tga or .dds). In this case you want everything except the lines to be invisible so the scroll or book texture can be seen underneath. For full color plates, you can simply block out the whole image, but for line drawings, or anything else that you want the paper texture to show up underneath, you want to use an alpha channel like this one. In fact, for this line drawing, the alpha channel is doing
all the work. The actual image is just a black square, that way the antialiasing on the alpha channel picks up more black and not some other color that you don't want to show up on the scroll.
This is the alpha channel: http://img714.imageshack.us/img714/1097/alphaexample.jpg
As mentioned before, in this case the actual image is just black. The alpha channel is completely determining what the drawing will look like. If you're using colored images, you will want the alpha channel to block out the image like this, but you would still have an image, and not just a black square. If you want the drawing to look more sepia toned, like Illuminiel's scroll, you would either keep the drawing as is, or fill the entire image completely with a layer of sepia tones. The alpha channel would still be doing most of the work in the latter case.
This is what the finished product looks like in the game: http://img232.imageshack.us/img232/3636/mapsofv09.jpg
Also, check out a lot of the free font sites out there as well. There's a lot of decent free fonts out there, and a few good ones that look like hand printed lettering. Never settle for comic sans. Comic sans is the most maligned font on the planet for a good reason.