What kind of expertise is required to install a gas fireplace log?
I consider it a DIY project myself.  However, it may be more ambitious than it seems at first.


Gas line work.
Brick/masonry drilling/patching
Electrical wiring for high heat environment
Control system
Modification of fireplace and/or gas log
Possible flue revision
Several building authority inspections


Whether this should be a DIY is determined by obtaining and understanding the "building authority" requirements and regulations for your location.  Maybe they say that a NFI professional must do the work.  Or maybe they say "all work must be to X standard and inspected by Y".