Hi, many of the features you've listed sound very interesting. I can only speak from my point of view, and what I personally use, and would like to have as far as software features are concerned.
A databank accessable via the internet with thumbnails visible to all, after a simple registration.
The customer could then choose to buy the image and receive either downloaded data, or if necessary, a slide can be ordered. In the case of data, file format, and size should be flexible, and the billing should be done online as well.
Other features such as barcode and additional information (either from the shooting, darkroom or computer work) would be interesting, but for me, not practical, but for others willing to invest the time in keeping up with such a database certainly valuable.
The software must be available for both Mac and PC, and fully cross platform viable. Importing from various programs via plug ins, for FreeHand, Illustrator, PS, Quark as well as text programs is also a necessity.
Direct scanning and importing from digital cameras would also be helpful.
Order confirmation and billing via automated email response would be cool.
If I think of anything else, I'll let you know.