Just to tag on a question which Kevin might need to consider...
what are the best options for routing a gas pipe from one side
of the room to the other (particularly past a doorway)?

For me this is not an issue, my boiler is located in the utility room
and the pipework is surface mounted close to the ceiling hence easy to
get at. When I have finished all of the work I need to do in this
room, I might consider boxing the pipes in but in this particular room
the fact that the pipes are surface mounted isn't really an issue.