For the invoice you either need headed paper and offset it in system, settings, printing or don't use headed paper and let George give you a basic letterhead with your registered George details. You'll have to experiment.
With regards to the extras on jobs you'll just have to put it as an additional job or in the notes of the job. That part of George has never really been sorted but overall its one of the best things I ever bought for window cleaning. I'd also get a cheap palm with cradle off ebay and get pocket George. It'll sync up and make it a lot easier.
If you get really stuck I would just email Paul at George support. He's normally very promt with his replies but his wife suffered a stroke recently so he may understandably be a bit slower at the moment.