Thanks again.

On second look, it's only the front brake cable that's at the end of its adjustment, and I can just loosen off the nut/bolt clamp and slide it further up for now.

I've fixed the problem with the gears not selecting, I'm not going to say what it was as it's too embarrassing. Suffice it to say that it was 10pm by the time I'd finished the initial unpacking, re-assembly, wipe-down and photos, and that beer was involved.