I've got the same Casseroll but just bought the frame and had it built with my own selection of parts. That said, you shouldn't be having shifting and braking problems if your LBS set up everything right. I put inexpensive Tektro 720 brakes on mine and quickly replaced the stock pads with Kool Stops, which made a huge difference.
If you want a front bag designed to fit your Casseroll front rack, check out the Zimbale bags, which come in black or olive green with brown leather trim. They also make nice seatbags that are basically knockoffs of Carradice bags.
http://store.zimbalenorthamerica.com...ex/10114.0.1.1