The reason why i need to use fire wire is because the software i am using will only connect to the camera through that.
I need to stream the video so that the software can sync the video with some other footage we are doing at the same time.
About the batteries, I could have more of them and switch when needed.
Using cable for power is going to difficult as the person using the camera must be able to move around a lot.
My backup solution is to simply use a normal helmet cam with recorder, but then i will have to sync the footage afterwards.
I hope this answers everything.