Merseburg POW camp/ LCpl J R Booth, G/15554

[Lyffe]

I have recently discovered that my paternal grandfather, LCpl J R Booth (G/15554) of 7 (Service) Battalion Royal East Kent Regiment, was captured at Vendeuil on either 21st or 22nd March 1918, and subsequently sent to Merseburg POW Camp in Saxony.

A search of the Internet describes Merseburg as being:

An assembly camp holding up to 25,000 prisoners, from which men were drafted to work camps.

1. What does this actually mean, and what were work camps?

2. There's an image of the camp in 1914 on the Internet, which reveals that at that time it was expected to accommodate 10,000 men (http://www.awm.gov.au/collection/P06889.007). Does anyone know if any later WW1 photo(s) survive?

3. How soon after the Armistice would the men have been repatriated to the UK? I'm just after a ball-park figure as I imagine they would have returned in batches.