Well Big Dave went to the vets.
Lung sounds are all normal (always nice to have what I've observed confirmed by a vet!). Throat sounds (around the level of the larynx, so consistent with losing his wheek?) were a little squeaky. Nothing to warrant bombarding him with antibiotics yet though, mutual decision made by myself and the vet.
As for his almost odematous abdomen... He has lost weight, about 30g in a year, but I have been trying to get him to lose some and have been monitoring closely. He's lost it gradually and has been at a stable weight since April, but he seems to have lost weight from his upper body during his "diet", and still has quite a round abdomen. He almost looks like a pregnant sow. The vet agrees that this isn't quite right, but he has no fluid wave (basically, tapping on his abdomen didn't produce any fluid movement, like ripples almost, it was just soft squishy intestines), and there's no palpable lumps or anything untoward. Again, I've examined him and couldn't feel anything either.
So, the verdict is to monitor him for now. If he deteriorates in any way, then obviously he's going straight back, Ian the vet has said if its out of hours and the other exotics vet isn't on duty, to call him directly and he'll see him. If he's ok and doesn't deteriorate, he wants to see him back in a fortnight to re-examine throat sounds, palpate his abdomen and see if there's any changes etc.