I may get some flak for going auto
I doubt it, autos are the bee's knees for turbo cars
In for answers, I've only built up some older american transmissions. Looked into doing up an 01M, but decided on a 4T65E for better ratios, not that it helps you both being transverse.
I'd imagine the ZF ones to be pretty similar to building up the older three speeds though (stuff in as many frictions as you can make the drums hold, drill out carefully figured orifices in the separator plates for quicker shifts, and put the line pressure through the roof to hold more power).
There's a .pdf that comes up in google first thing searching "zf 5hp19fla", shows some good exploded diagrams. Looks like they've got a lot of different clutch drums available depending on application. Maybe grab up the biggest meanest audi application one you can find cheap on craigslist or in a junkyard, raid it for the drums that'll hold more frictions. Use your TDI specific final drive gears.
I'd link the pdf, but google's gotten real streamlined lately, gotta figure out how to get the dang URL out of their garbage redirect link.
ETA5: maybe this one will work...
www.zf.com/global/media/zf_media/document/int_print_catalogs_documents/usa_4/5HP19FLA.pdf