There are a couple of GUI tk interface creators like Zooz but I find it easier to just add the code by hand as I build up the interface. One of the major drawbacks of Tk is that as the application gets larger and more complicated you tend to end up with global variables all over the place. There are object oriented solutions to this but I generally end up using hashes for them. Oop and I don't get along well, one of the reasons that I still use perl for most things that I write and haven't really gotten into python where everything is an object.
Here are a couple of links for some basic Tk info. There are many around the web.
Tk tutorial
Zooz My opion though is that it easier to just code the ui.
Some more advance widgets.
Oh and I'm still tinkering with this some but I think I'll be moving to an epub like storage system for my books. Where the book is exploded into an oeb style structure with either mobi2oeb or convert lit then modify the opf file and build an imp with a short windows script that wrote that uses the BookMill com interface. From there I can store the imp file and all of the other files in a single zipped archive or possibly bzip2. That will give easy access to the created imp file so it can be copied to my bookshelf or to easily change the metadata in the opf and rebuild the imp. The impfindGUI script will most likely be the starting point with some modules added to handle manipulating the book files.
The sort for the path and the button on the shelf tab shouldn't be hard to add. I'll look at adding that to the what I have and post another version in a couple of days.