I've managed to get still capture working... the issue seemed to be with the SD card interacting with gPhoto.
Still, streaming is a problem. I've captured a full log file. I believe this is also a gPhoto bug - the camera supports two modes, PTP and MSC, and only MSC allows full communication with the computer. However, the camera then shows up twice, once as an MSC device and once as PTP. Looking on other forums, it appears that entering preview modes is buggy for some cameras with "forcing the mirror to go up" and a list of cameras requiring special management is in the source code. Perhaps adding this there would help?
Full log file attached: