So I got a little further last night. Turns out the bootloader I was trying to flash was the wrong one, this was the one linked from the GitHub so that may need correcting or I just have completely misunderstood what was written there.
Anyway, once the correct bootloader was flashed and firmware I get a constant flashing LED.
But still firmware :null.
I also cannot change the Node ID or Speed as it appears to be constantly refreshing, so as soon as I select the drop down box it refreshes and deselects.
It's progress but not as much as I'd hoped....