Cargo Bikes

Evening. LFGSS hive mind help request pls.

So i have had a Bafang motor installed on my Bullitt. Thanks to @Chalfie for his help via DM. I went with Besbike in Greenwich. Their main guy Alex is not there at the moment, an assistant is looking after things in his absence. Wish I had waited until Alex was back.

So first up the cabling was hooked up through the frame, the rear part of the cargo area. This meant if I mounted anything like a box, the cables would be crushed. Had to remove everything from the cockpit, put the cables back around, tie them up, and put everything back on again. Not a huge job, but still a bit of a pain in the arse.

Second thing was the little start button for motor and the display seemed a bit stuck - had to really push it in (and felt a little "pop") to get it to start up. Seems to be OK now, thankfully, but my nerves werent happy with wondering if I'd broken something.

Next was with the chain. As soon as I collected it I could see that it was way too slack. See the attached photo. I asked the assistant immediately, explaining that it was going to get worse as time went on, as the chain stretched. He said at that point I could take a link out myself. Which isn't really the point if I've paid you to do the work mate... and my 1/8" chain breaker is snapped anyway. (I've managed to get a lend of one this evening)
I think they could have taken out one complete link and the rear wheel would still sit in the axle OK.

There are some minor problems with the gear shifting properly in the mid-drive motor, when it's at 4th and 5th gear. After taking it out for a few spins, and listening and feeling for the changes, the only thing I can currently put this down to is the lack of tension in the chain.

I asked SBC about it, and sent them the pic. Jamie responded to say "They haven't even put the angled washers on the right side - Your gear cable shouldnt be in that spot. I have a (half link) 3/32 chain here that will suit, but you should have enough room on the drop out to adjust and set up to not need a half link."

I only had the Nexus 5 a few days before bringing it to Besbike so I can't remember what it looked like. Looking at the way my Alfine 8 is set up, from what Jamie is saying, I'm assuming the gear cable housing on the Nexus 5 should be ran along the top tube & seat stay, rather than the frame underside & chain stay? And where the gearing cable goes into the hub, that little "arm" (don't know what it's called) should be more vertical rather than horizontal, as it is in that photo?

SBC said they could look at it on Saturday but now I can't go up there, kids blah blah etc. So I might have a go off it myself tomorrow on my lunch break. The next steps in my head are

ONE: Take the grip shifter off the handlebars and remove the zip ties along the underside of the frame
TWO: Loosen axle nuts and slide the wheel out if necessary, so I can turn it 90', and then run the cable housing along the seat stay and the top tube
THREE: Slide the wheel back in, then remove a link from the chain. Realign the disc brake caliper if necessary

I'm still pretty much a noob with nexus 5, Bullitts, motors etc. so any advice especially welcomed. I've looked for a pic of a Nexus 5 setup on a Bullitt online but can't find a closeup so unsure about whether the housing needs to be rerouted.