We've just sent our stuff over via SevenSeas move cube service so did all the packing and manifest ourselves and they just pack it in the cube and send it off.
Definitely agree with the cleaning comments - we scrubbed my partners bike wheels with Jayes fluid and a toothbrush to try and make sure there was nothing there. fingers crossed it gets let in!
We sent our washing machine over too but ditched the dryer and other white goods (they were built ins so went with the house sale). Sent my vaccuum over too but I'm not hopeful of actually getting that back even though I took it apart and cleaned every inch (took a good 3 hours). depends how much time you want to commit to really.
For the manifest, the example sheet they gave us was pretty basic e.g. Item 1 - Brown Box - Books, Item 2 - Bedside Table - wooden etc. I would advise keeping anything they might check to one side and putting all together in one box to make things easier.