It turns out nothing was broken. Somehow the rectangular connector between the battery cable and everything else became disconnected. Picked up the error this morning and saved myself a trip back to the bike shop.
Pictures (And numbers).
It's the Solarbike rebranded 48v 500w version. I don't think I need the power, but after reading this thread I thought I'd go for a younger model(?)
I've coupled it with a 48v, 10A Tiger Shark battery. The Cruzbike Quest's 451's e-ring is now sitting in a box: The new crankset has longer arms, but they also appear to be slightly more offset, which is helping with the 'heel clipping the derailleur' issue I had. The mid-drive comes with a little/compact LCD screen and a separate throttle, so I have options in case I injure my leg(s) I guess.
This is compared to my rear hub config, which was: Rear Hub motor (also 500w) with a 48v, 14A battery and throttle. Shorter 155mm crank arms and the e-ring. Weight was all in the rear.
I haven't ridden the mid-drive any distances yet, just a couple of trips down the street. At this early stage, I think I prefer the added weight and stiffness at the front, as it adds stability at higher speeds... but after a ride to work tomorrow I'll know if over a distance that stiffness comes at a cost to my arms and legs.
I'm worried about the lack of SRAM Anti-rotation washers (We've tightened up the washers that I do have significantly). I suspect that when the bike's previous owners had new wheels made, they forgot to put the anti-rotation washers back on. Shout out to Henry at Solarbike in Fremantle, Western Australia for spotting their absence. I suspect he's saved me a whole lot of grief.
I don't know what kind of distances a 10A battery will get me, but I can say that at the 2nd power assist setting (of 4), I could get into the 3rd gear+smallest ring and pedal (hard) at around 46km.