I'm going to be getting a natural gas bbq soon but need to know what sort of clearances I need between gas line and things like dryer exhaust and high efficiency furnace intake and vents etc before I can plan out deck and location of bbq

I think your major concern is the dryer exhaust. Lint coming out of that will stop up things like orifices on burners. You may be able to route the dryer exhaust down the side of the house and slanting down with an elbow and length of pipe. Don't screw it together; tape it with foil tape and support it with straps or two-hole clamps to house. You don't want dryer exhaust covering your deck with lint buildup because it gets on wood and sticks making it hard to remove.