The torque convertor uses transmission fluid and is filled by the transmission's internal pump. When you start out with a new convertor, it's a good idea to put a quart of fluid in before installing...
Dana 44s come anywhere from 2.XX:1 ratio all the way up to 5.XX:1s. After market you can get 6:1 gears for them. It just depends which vehicle they are coming from.
75w90 Gear Oil, preferably high-end synthetic (not just Mobil 1, but Redline or Royal Purple). Non 'open' differentials may require a friction modifier.