First answer - 4.5 to 5 litres .
Second answer - how long is a piece of string as there are many opinions on which oil to use . Personally I use either Mobil1 Motorsport 15w 50 , Millers CFS 10w 60 or Castrol Edge 10w 60 , depends on price & availability . Any good quality synthetic should be ok but don't use the 0w or 5w oils as they are too thin for the EJ20 engine .