This camera has 2 ports that seem to do the same thing. Only one is faster. (if I read everything correctly)
Well, HDMI is video and USB is data, but neither will easily do what you want.
A raspberry pi might work but I think I am better off finding a camera that works with less trouble.
Yes, that is probably the better approach. The PTP based approach would increase power demand, weight and complexity, and the live view is pretty low quality.
If you're looking for CHDK supported cameras and standard def (NTSC/PAL) video is sufficient for your FPV needs, you can check the manual (available from Canon's support site) to verify that it supports TV out in rec mode. If it does, it will be mentioned in the section on TV, like "When the camera and TV are connected, you can also shoot while previewing on shots on the larger screen of the TV" (the SX610 is an example)
If it doesn't support TV out in rec, that section of the manual will only describe playback and not mention shooting. CHDK can enable standard def TV out in rec for some cameras that don't support it natively, but it's only implement on a few cameras, and it might or might not be possible on others.