Sorry! I was meaning to reply to this!
So the good news is that the food got cooked. Perhaps not perfectly but it didn't get burned to a crisp and nobody got the shits.
There was a lot of food to cook on a not-huge BBQ, so the less drippy stuff had to go on over the charcoal, with the drippy things over the drip trays. This was good in that there weren't really any major flare ups - however, it did mean that the cover had to come off relatively regularly to keep the stuff over the coals moving so as not to get burnt. This meant that the oven effect of having the lid on didn't work quite as well and it took longer than anticipated for the stuff over the drip trays to cook. It also means that it doesn't brown reassuringly which, for a novice with no meat thermometer, was a little unnerving.
Could have got away with putting stuff over the coals later, but food that was ready earlier just got piled up in a foil tray, covered in foil and placed in a warm oven. Meat needs to rest before eating doesn't it...?
So all in all, a success; but more practice needed on my part. Would be really easy to get right if doing food for fewer people.
Thanks for your help, Lagers