Yes they were outfiiting and doing wing fix at the same time in 261-266. The British guys who were doing the wing fix were only sometimes shouting something you couldn't understand before riveting so you knew you had to put your ear plugs in. I think I didn't see any scaffolding around the wings in the bays 213 and 214 the one or two times I walked trough there.
Yes, sometimes I saw one of them empty...looks really impressive. I think at the family days in August 2005 visitors were allowed in there. Anyone who has photos (I was a little child at this time, so I don't have any)
Some are also speculating whether A350s might be painted in there. They already painted a A340-600 for Etihad from what I know in there:
For everybody to enjoy, even not eagle-eyed spotters can now have a look from above at Finkenwerder plant on Google Earth, there is an image updated on July 2013, in which HL7621 and another EK frame can be admired on the flightline.