Gas Dryer

Its easy enough to do.  I would only replace the gas line extension if it appears to be in poor shape, crushed kinked etc..  Check the gas line for leaks as already suggested. Make sure you have a good quality dryer vent hose.  Older ones were made of vinyl and susceptible to fire.  If possible take the time to replace slinky style dryer vent hose with a solid pipe.  Solid pipe doesn't catch lint like the slinky type hoses. 

HTH

Agree to above.  WRT the vent ducting,  Mydryer vent to the outside was above the dryer, I found some 4" diameter grey plastic pipe (I think it was sewer vent pipe) and added a few elbows.  It slipped together great and since I did not glue the joints its easy to check for lint build up.  All I need to do now is add a shelf on the wall so the gap between the dryer and wall is coverd and usable for laundry supplies.