Re the volume reduction, vapour to liquid - don't know the ratio...

Re the volume reduction, vapour to liquid - don't know the ratio but you can get a feel from the energy equivalent of gas:oil.

The energy equivalent used by TXN is 6,000 cfg = 1 bbl

a barrel = 5.61 cu ft (actual volume of liquid content, I believe).

So, there is a fall in volume through liquefying of about 1,000 to 1. Somewhere in that region.