You said you wanted comments, so even though I don't generate much pdf, here goes.

I don't like writing in XML. It's ok as a data interchange language in which case I use TT to fill in the variable bits. Coding in XML is painful (I've used ANT and XSLT). Please don't make me use it for coding.

I like the idea of a TT plugin or several of them. There is always an advantage to a system people understand and like. But your third option might work too. Perhaps you can conceive of a little language which is easy to write and parse that is still flexible. I've recently been at work on a little language which describes web apps. It uses simple named blocks. Your situation is more complex, but maybe something like that could work.

Phil