I love a good argument... Uh, i meant discussion ;-)
I was thinking of using PHP, MySql (or another database that's more appropriate), and
pdflib or
ClibPDF.
pdflib source is free, and only commercial use on a server requires a liscence (which is pretty hefty at a minimum of $500, but peanuts for a large pdf distributor).
clibpdf has a similar liscence, but commercial use starts at $1000.
And i'm not even tlking about development costs here. But as a private project it wouldn't cost squat and would give you the ability to play with it without buying expensive programs. It's especially interesting for people who do not want to sell pdfs commercially...
Making good templates is a lot of work, but the strength of templates is that it could be used for more than one book, just look at the D&D line...
As for multi-version tracking:
1.) Could sell them as seperate items (i would hope that they can keep track of that).
2.) Give the buyer the option which one(s) to download and hope that RPGnow will give you their download log.
Database driven pdf generation is a still unknown Utopia. If you want to do multi-version pdfs your better off doing it manually (takes 15 minutes tops extra). As for extra costs for downloading extra and larger files, GBs are not that expensive anymore and a few cents extra per product will help you a long way to cover the costs...
Landscape vs. Portrait, not really an issue i think, mostly because it's pretty counter productive for printing and most of the navigational tools are already on the leftside of the screen.
Let the hijacking commence!!!