Okay, here are a few responses:
Widest is the Schneider Super Angulon 72mm XL. Awesome lens. Use with colour/B&W NEG and it doesn't need centre filter (well, not really). Will probably need it for transparancies.
Try http://www.3c-store.cn/ for DaYi "stuff".
I have owned the DaYi 617 Shift and found it a very good camera. But the whole nose cone thing annoyed me, so had Shen Hao design and build a 6x17 field camera (now sold as the TFC617-A). Kills the DaYi on weight, lens options and flexibility.
Mind you, if I was to start again, I'd get a 4x10 for Pano work and get a 4x5 reducing back for other times...